http://realgm.com/src_wiretap_archives/57324/20090217/cavaliers_discuss_trade_for_jamison/ Interesting. I don't know how much better they'd be.
I think adding Jamison would help the Cavs. Obviously not as much as adding Stoudemire would, but it would still help them all the same. I think he'd fit into the system pretty well - he has a nice jumpshot, rebounds well and has vastly improved his defense. However, whether he provides the Cavs with anything to put them "over the top" is another matter. He would improve them, but I don't think he gives them that extra dimension that they need (and might get from a player like Amare Stoudemire) to win that championship.