It wasn't nearly as dramatic as the time when Andre Dawson agreed to play for the Cubs for 1 year at whatever salary they'd pay him (1987), but Adrian Beltre's 1-year stint in Beantown served the same effect – a power hitter in his early 30's convinced at least one team that he was worth a lucrative contract. While Mariners fans enjoyed his scintillating defense enough that the team included a spot entitled, “The Great Wall of Adrian” for the 2006 season (http://mlb.mlb.com/sea/fan_forum/commercials_2006.jsp), many still have the impression that he only plays for contracts. This “contract season” position is defensible, as he's only topped 3.7 WARP twice since 2000, and both seasons have been over 8.0 WARP in contract years. On the other hand, it may only be happenstance, as he was “playing for a contract” in 2009, and posted a 2.0 WARP.
The Rangers are hoping (and wagering a lot of money) that Beltre's struggles in Seattle and his successes in Arlington (career .306/.336/.521 in Texas) are due to something other than monetary motivation (and questionable Texas pitching for most years). Adrian's two best seasons have included both better contact skills (K/PA rates of .145 and .139, compared with a career mark of .170), and more success on balls in play (.334 and .321, vs. a career BABIP of .294). While there's no “Green Monster” in Texas to help Beltre lead the league in doubles again (49 in 2010), he has a decent shot at equaling – or bettering – his 28 homers from 2010.
Normally, when a ballplayer has amassed 7518 PA, there's not much debate over how good he is, but Beltre is an exception. He's still essentially in his prime years, entering his age-32 season in 2011. If the “motivated” Beltre shows up in Texas for the life of his contract, and he keeps playing until he's 40, it will be hard to keep him out of the Hall of Fame. But many will avoid him completely on auction day, as he hit just .266/.317/.442 in five years in Seattle, finishing in 2009 with a putrid .265/.304/.379 batting line. This camp will dismiss the Boston stats as some sort of Fenway Fluke.
While it's rarely good to overpay for a player, the wisest course with Beltre is probably to assume that his performance variances are due mostly to random sampling, and to bid aggressively on the power-hitting third baseman who will be playing in a good park, surrounded by hard-hitting teammates. He doesn't walk much, so he's worth less in OBP leagues, but his contact skills and propensity to rifle extra-base hits suggest that he could even help a fantasy team's batting average, despite all those sub-.280 seasons in Seattle. A .300-30-100 type season – ala typical Aramis Ramirez – would not be shocking at all. For those concerned that he's only reached 30 homers once in his career, recall that he also hit 25-26 homers three years running while calling Safeco his home park, a feat roughly equivalent to hitting 30 homers playing for Texas.
The average MLB first baseman hit .264/.350/.452 in 2010. For those familiar with baseball-reference.com, that came out to a tOPS+ score of 120, or roughly 20% better offense than a league-average player. From 2006-2009, Adam LaRoche hit .276/.349/.500, but due to playing in good hitting parks, that also came out to an OPS+ score of 120. With roughly average defense and full-time gigs over those four seasons (albeit with numerous teams), his WARPs were 3.6, 3.3, 2.5, and 3.4, respectively. There's nothing wrong with being a “league average” player, since there are only 30 teams, and perhaps because he was so persistently average for such an extended period, analysis could be easily found which overrated him and also analysis could be found which underrated him.
Of course, LaRoche slumped to “below average” in 2010, hitting just .261/.320/.468 (106 OPS+), and failing to make one of his well-known 2nd-half surges. He's hit .295/.354/.535 in the 2nd-half for his career, compared with .252/.327/.449 in the first half; in 2010, he hit .269/.307/.481 in the 2nd half, compared to .253/.331/.456 in the first half. Coming to Washington won't do him any favors. San Francisco's killer rotation will be replaced with Philly's, and his home park will be much less favorable to his left-handed pop. All-in-all, there's not much reason to expect anything different from almost-average play in 2011.
For fantasy contexts, mediocre players can vary wildly in value, depending on environment. Jayson Werth and LaRoche may be better defenders than Josh Willingham and Adam Dunn, but the big guys' offensive contributions will be missed. Barring amazing growth spurts from the young middle infielders and Wilson Ramos, it's difficult to envision the Nationals scoring the additional 0.29 runs/game they'd need to be league-average. LaRoche (and Ankiel to some extent) will help balance the predominantly right-handed offense, but don't expect fertile gound for runs and RBI for LaRoche here. In most leagues, LaRoche should be viewed as “replacement level”, a guy who will play every day and not be awful.