Fielders bat would be a great improvement to this lineup no doubt. There isn't that big of a need for first baseman next offseason, as the Yanks have Tex, Boston with A-Gon at 1B, Ortiz at DH; I don't see Tampa spending that kind of money. The Orioles were active this offseason, and we have seen them make big signings before. The White Sox are locked up with Konerko and Dunn. Detroit is locked with Cabrera and V-Mart. Dodgers could be suitors, though their situation is messy right now so who knows what the future holds. Cubs might be suitors as well, since Pena is only on a one year deal. Plus Pujols could become a free agent if the Cards don't resign him to an extension, so I'm sure that will have an impact.
I think Fielder would be better suited for an AL team because at least later in the contract he could DH if his defense declines.