Let's compare two players:
Player A - 24 HR / .250 BA / .342 OBP / 111 OPS+ / 246 TB
Player B - 36 HR / .267 BA / .384 OBP / 134 OPS+ / 285 TB
Player A is Mike Cameron and Player B is Jason Bay. Clearly Bay's offensive numbers are better across the board than Cameron's. Some players benefit greatly from Fenway Park's Green Monster and clearly the Red Sox front office feel that Mike Cameron is one of those players. It is reasonable to expect an increase in HR from Cameron along with an increase in doubles (wall-ball hits combined with Cameron's speed). Probably positive thinking on my part but I really can foresee Cameron coming close to matching Jason Bay's total base mark from last season.
EDIT: Very interesting comparison of Bay and Cameron done a couple of months ago. The bottom line conclusion they drew was that Cameron was actually the better overall value.