In 2009, the Yankees used 22 fielders and 23 pitchers plus Nick Swisher.
Take the core lineup out of the discussion for a minute. In the Yanks' case, that's the Posada, Tex, Cano, Jeter, Arod, Damon, Gardner, Cabrera, Swisher and Matsui plus Sabathia, AJ, Andy, Joba, and Mo.
The remaining players contributed 6.4 wins above replacement in 2009, with Phil Hughes the top contributor at 3.2 and Chien Ming Wang the unsurprising laggard at -1.9.
Leaving aside the Red Sox 9 starting hitters plus Victor Martinez and the main pitchers (Beckett, Lester, Penny, Wakefield and Papelbon), the remaining Red Sox were worth 7.6 wins. Clay Buchholtz contrinbuted 2.5, Okajima 1.9, Ramon Ramirez 2.8 and Takashi Saito 2.7. Incredibly, their worst performer was a three way tie between Tazawa, Smoltz, and Javy Lopez at -0.6.
The Angels starting 9 joined with Lackey, Weaver, Saunders, Santana and Fuentes combined for 45.5 wins on the way to the biggest margin of victory in the AL. The Angels' bench contributed only 5.6 wins, led by Matt Palmer's 121 innings and 2.8 wins (about 9 times more valuable than Vlad Guerrero) and held back by Gary Matthews Jr.'s -1.4 wins (great FA signing there).
Should the Twins simply be given an annual Most Efficient 40-man Award? They used a floating lineup, getting fewer than 100 starts from 2B, 3B, SS, LF, and DH. For those positions, I pro-rated the top 2 contributor's games at each position. Then I took out the wins for the Twins top 5 starters and Nathan, since Slowey and Perkins combined for 187 innings. That left an incredible 11.6 wins from the remaining Twins. The rest of the bullpen alone was worth 6.6 wins (more than the whole bench on any other team), that's how incredibly dominant they were throughout the regular season. Joe Rauch's rock solid 17 games were worth another 2.1 wins, and Pavano pitched in his 1.3 after the deadline. What saved the Twins' season is that their few negative performers were only slightly negative (max -0.3), except of course Alexi Casilla, who spend most of the season as the 2B, giving him time to rack up a -1.3.
Back to the heart of the question, did the Yankees get good value for their money?
I say yes, with plenty of room to improve. On the one hand, Jose Molina's $2M salary, Nady's $6.5M, Marte's $4M and Wang's $5M wasted (regular season) salaries are nothing to sneeze at. Plus, the addition of Jerry Hairston Jr. to bolster the injury ravaged bench didn't come free. As we see from Cervelli, Gardner, Houdini, Coke, etc., the best help is the help you train yourself. A stable of young players able to fill the gap when a Wang or an Arod goes down is essential to a cost-effective strategy. Building the Opening Day lineup this way leaves payroll space to add a Hairston when the opportunity arises midseason. A Hairston or a DeRosa might be incredibly attractive, but putting Nady's salary in the bank might be the wiser long term approach.
And we shouldn't be misled by the Yanks' (comparatively) low number of wins off the bench- the quickest way to stack up WARP is to pitch a large number of effective innings. The Yanks didn't have to turn to a Smoltz or a Pavano to save the season. While Mitre and Gaudin certainly were given their chance, because the Bombers were in such a strong position for most of the season (leading the division from July 21st onward and on cruise control after sweeping Boston Aug 6-9), the Yanks didn't need to shuffle through 5th starters or rush minor leaguers to the Show.
Ultimately, the best way to get the most out of the 40-man roster might be the most obvious and most unattainable method: keep the starters healthy.