If Mo Williams is healthy, this is a big pickup for the Cavs. One of their biggest problems has always been the failure to get scoring from anyone other than LeBron. Williams is a guy that, not only can score, but he can create for himself and others.
They also still have Wally's expiring contract.
It's true that the loss of Joe Smith should not be overlooked, but if you watched the playoffs, as much as Ben Wallace has regressed in the past few years, he is still a much better defender than Joe Smith, and he defended KG much better than Joe Smith.