Prime is overrated. Barton G is better. If you like sushi go to Bond Street. If you want to make the trip to Coral Gables there are great restaurants there. Francescas, which is number 1 in zagat is ridiculous. Its like a peruvian/italian fusion. There is also cafe vialetto, which has the best desserts ever, on top of a great meal.
For long on the beach go to alton to Taste. Most things on South Beach are in fact, overrated.
If you want a great meal, just go to Joe's Stone Crab. Don't forget your wallet.