First of all, the Phillies just added a future hall of famer in spite of Thome being at the twilight of his career. If he serves just as a pinch hitter, his years of being around the game will benefit his teammates. He will be great in the clubhouse.
He will provide more than that though. I know its been years since he played the field at any regularity. But he will work out at first base in spring training and I predict he will get the bulk of the playing time at first base until Ryan Howard returns from his ACL injury. He will benefit from playing his home games at Citizens Bank Park and will hit some homeruns. Also, he will not be batting 3rd or cleanup like his last go-around; more like 6th or 7th. Furthermore, the Phillies are in the market for a third baseman and left fielder and are interested in spending some money this offseason. Reports are that the team is shopping Shane Victorino and there is still a good chance Jimmy Rollins doesn't return next season. To me the Thome signing will turn out to be a bargain.
Lets not forget about Thome's relationship with Phillies manager Charlie Manuel. The two of them go back to when Manuel and Thome were both in the minor leagues with the Cleveland Indians. Thome has always been a Manuel favorite and he will be used in a way where Manuel gets the most out of him. As much as I may regret saying this being a Mets fan, Thome playing almost every day to start 2012 will be one of the better stories of the beginning of the 2012 season.