Again, how much a player cost (be it by trade or free agency), his long-term impact, or how the player(s) he's replacing are likely to perform in the coming season are not factors. This is simply a comparison of the 2009 production each player is replacing to the 2010 production he's likely to contribute. Also, note that the statistics used below (VORP, UZR, SNLVAR) are all adjusted for context, rendering park and league effects largely moot for our purposes here.
The Brewers' failure to return to the playoffs in 2009 was directly attributable to the collapse of their starting rotation. In 2008, Ben Sheets, deadline additions CC Sabathia, David Bush, Manny Parra, and Jeff Suppan were worth a combined 21.1 wins above replacement per SNLVAR (Support Neutral Lineup-adjusted Value Added over Replacement, Baseball Prospectus's win-probability based stat for starting pitchers). In 2009, with Sabathia and Sheets gone, Milwaukee's top five starters (Yovani Gallardo, Braden Looper, Suppan, Bush, and Parra) combined for just 7.9 wins above replacement, most of that from Gallardo.
Enter free agent lefties Wolf and Davis, who replace free agent Looper and either Bush or Suppan, who will fight for the fifth spot in camp. The two displaced '09 starters were worth roughly a win each in '09. Davis, an innings eater who had some success with the Brewers from 2004 to 2006, is typically a four-win pitcher. Wolf, who has battled injuries in the past and is coming off a fluke season buoyed by an abnormally low opponents' average on balls in play (.256 against a league average of .298), was worth six wins to the Dodgers last year, but is more likely to also be a league-average pitcher if healthy, worth another four wins. That's a three-win upgrade at each of two rotation spots, though it still leaves the Milwaukee rotation well short of its 2008 performance.
Estimated combined upgrade:6 wins
One reason the Twins needed 163 games to overtake the Tigers in the AL Central last year was that they failed to field a viable middle infielder until trading for Orlando Cabrera at the non-waiver deadline. Prior to Cabrera's arrival, the Twins' shortstops (primarily Nick Punto and Brendan Harris) hit .247/.303/.339. Their second basemen (including Punto, Harris, Alexi Casilla and Matt Tolbert) hit .209/.302/.267 over the full 163 games. Adding to the problem, the two positions were a combined 16.5 runs below average defensively over the course of the season according to Ultimate Zone Rating (UZR), primarily due to Casilla and, surprisingly, Cabrera. The net result was that the two positions combined to be roughly two wins below replacement level.
The Twins haven't had a quality veteran at either position since trading Chuck Knoblauch after the 1997 season, but this offseason they finally threw some money at the problem, signing Orlando Hudson and bringing in arb-eligible former All-Star J.J. Hardy via a trade with the Brewers. Curiously, both are valued for the wrong reasons. Despite his reputation, Hudson hasn't been rated above average in the field by UZR since his last year with the Blue Jays in 2005, and Hardy's bat went limp last year as he hit .229/.302/.357 at age 26, ultimately losing his job to shortstop prospect Alcides Escobar. Still, even if his bat doesn't recover, Hardy's underrated defense could be as much as a two-win upgrade for the Twins, and Hudson's bat is generally worth 2.5 to three wins above replacement at the keystone according to VORP (Value Over Replacement Player, Baseball Prospectus's total-offense stat expressing value in runs created above that of a replacement player at the same position, with 10 runs roughly equal to one team win). With average defense, Hudson could be a three-win upgrade, and if Hardy can recover to be a league-average offensive shortstop, he could be a three-to-four-win upgrade at shortstop, though a more modest recovery for Hardy might be a safer projection.
Estimated combined upgrade: 5 wins
Last year, the Diamondbacks' first basemen (including Chad Tracy, Tony Clark, and rookies Josh Whitesell and Brandon Allen) hit just .228/.321/.396, and only did that well because third baseman Mark Reynolds did some of his best work while moonlighting across the diamond, hitting .323/.400/.591 in 105 plate appearances while at first. The net result was that the position was a half-win below replacement for the season. LaRoche, who split 2009 between three teams, has hit 274/.343/.491 on his career, which makes him an almost perfectly league-average first baseman. As we've already seen above, an upgrade from replacement level to league average can be a significant one. LaRoche is typically a 2.5- to 3-win player, making him a more than three-win upgrade for the Snakes. The catch is that Allen is a significant prospect who hit .324/.413/.641 for the D-backs Triple-A team in Reno last year, and LaRoche is a notorious slow starter (career .252/.326/.447 first half, .300/.363/.546 second half). To get LaRoche's full value, Arizona will have avoid the temptation to give the job to Allen at mid-season. Then again, if Allen delivers on his promise, he could deliver the upgrade himself.
Estimated upgrade: 3.5 wins
The Nationals were two runs allowed shy of matching the Orioles for the most runs allowed in baseball in 2009, so any respectable pitching acquisition would have to be an upgrade. Marquis, a groundball-inducing innings-eater who made his first All-Star team last year, qualifies as a respectable addition. He'll replace rookie Jordan Zimmerman, who could miss most or all of 2010 following Tommy John surgery, departed veteran Daniel Cabrera, and let's say the seven starts the Nats received from 23-year-old Collin Balester. Those three combined for 31 starts in 2009, posting a 5.37 ERA in 166 innings, a performance that actually rated as a pinch above league average (0.2 wins) per SNLVAR, mostly thanks to Zimmerman's solid work in half of those starts. Marquis's typical 200 innings of league-average work are worth about 3.5 wins above replacement.
Estimated upgrade: 3-plus wins
It's impossible to project with any degree of confidence what Oakland will get from Sheets, who hasn't thrown a major league pitch since September 2008 due to a torn flexor tendon in his pitching elbow. He looked good enough in workouts for the typically thrifty A's spend $10M on him for the 2010 season with additional incentives for every ten innings from 165 to 195. Sheets hasn't been healthy for a full season since 2004, but if he's able to repeat what he did for the Brewers in 2008, he'd be worth six wins above a replacement starter per SNLVAR. Last year, Josh Outman (out until at least mid-season following Tommy John surgery) and departed swing men Dana Eveland, Brett Tomko and Edgar Gonzalez combined for 33 starts, posting a 4.78 ERA over 169 1/3 innings, a performance worth 2.5 wins over replacement, largely due to the fine work by Outman and Tomko. The 2008 version of Sheets would still be a 3.5 win upgrade over that quartet, but as with Hardy, let's hedge our bets a bit. Sheets was four wins above replacement in 2007, when he threw just 140 innings. Let's split the difference.
Estimated upgrade: 2.5 wins
The 2009 Red Sox's dirty little secret was that, save for the perpetually underrated J.D. Drew (10.5 runs above average in right field per UZR), their outfield defense was a disaster. That Jason Bay was 13 runs below average in left field may not have been a huge surprise, but Jacoby Ellsbury, having finally taken over center field full time with Coco Crisp in Kansas City, was even worse. Ultimate Zone Rating listed Ellsbury as 18.6 runs below average in center, a shockingly poor performance for a young player known for his speed. Together Bay and Ellsbury cost the Red Sox three wins in the field, which is one reason why Bay was allowed to sign elsewhere and Mike Cameron was brought in to play center and push Ellsbury to left.
Cameron's center field defense has been worth almost exactly a win for the Brewers in each of the last two seasons, while Ellsbury played 346 1/3 innings (less than a quarter of the time he spent in center last year) in left field in 2008 and was nearly a win above average in that brief time. Don't expect that sort of brilliance from Ellsbury this year, but even if he is merely worth one win over a typical 1,200 innings, the Red Sox could experience a whopping five-win upgrade on defense alone. Some of that will be given back in the downgrade from Bay's bat, which was worth five wins in 2009 according to VORP, to Cameron's, which is typically worth roughly half of that, but that massive upgrade on defense keeps the Sox's new outfield arrangement well above replacement, and well above their 2009 performance.
Estimated upgrade: 2.5 wins
Amid an otherwise well-stocked team, the 2009 Red Sox struggled to keep their heads above replacement level at shortstop. They only managed to finish the year three-quarters of a win above replacement at the position because of the deadline acquisition of Alex Gonzalez, whose .284/.316/.453 performance for Boston blew away those of his immediate predecessors (Jed Lowrie, Julio Lugo, and the living embodiment of replacement level, Nick Green), who hit a combined .217/.289/.324 in 463 plate appearances. Replacing that quartet in 2010 will be Marco Scutaro, a veteran utility infielder who last year, at age 33, had a starting major league job on Opening Day for the first time and responded with a career year, setting personal bests in batting average (.282), on-base percentage (.370), and slugging (.409), contributing four wins above replacement to the Blue Jays' offense while playing solid defense. Scutaro seems unlikely to repeat that production, but he should be able to match the defensive performance of Boston's 2009 shortstops (which, save for the stone-gloved Lugo, was good but unspectacular) while easily outdistancing their net 2.8 VORP. Even if Scutaro loses half of his 2009 production, he'll still be a two-win increase. Combined with Lackey, Beltre, and Cameron, Scutaro gives the Red Sox the potential for an improvement of a dozen wins based on those four roster spots alone.
Estimated upgrade: 2 wins