From a marketing point of view it does make sense for AC., they will make millions in Asia on Beckham. He has also shown he can come on the last 20 minutes and create chances to score. I think Beckham can still give you that option and the Italian league with it's slower pace might be the right move for Beckham.
As for Ronaldinho, while I don't watch the Italian league, didn't he score a couple of goals in their victory this weekend?
Regarding Kaka, while they could wipe out their debt, you don't sell great young players at the top of their game. Plus I don't understand how AC which are owned by Berlusconi who is almost as rich as Roman are having financial problems.