Ricky Davis is a good offensive guard, really athletic. Hard to guard, explosive, quick, etc. Downside? Bad attitude, sometimes a ball hog, has an ego, tough to coach, etc. Miami has enough leadership though to prevent him from doing anything too crazy.
Mark Blount is a mediocre center, not bad on D or offense. He isn't a bad player at all, but has a big & long contract. He is the main reason Minnesota did this trade, to get his numbers off the books. I'm not sure how much he will play in Miami, unless if he logs in some minutes at PF, which is possible. More then likely though, Zo and Shaq's minutes will be lowered a little for health reasons. You can usually bank on a little "vacation" in the middle of the season for Shaq, and they will be fine with Blount in there.
Value and talent wise, Miami wins big time. But if you look at the overall picture and include financial issues and contracts, it really helps both teams.