OK, I'm back in town and ready to offer my opinions on things!!!
OK, if free dessert is the objective, I can tell you the only place you're guaranteed to get one is the Plaza, and even then you may have to ask!

But they seem to pass out these birthday cupcakes like, well, candy!
As for the Wave - can you guys split a meal? That's our secret to eating at table service restaurants on the cheap. Even if you are a hearty eater, I guarantee that splitting a Disney-sized appetizer, entree and dessert will fill you up!
Whispering Canyon will be fun if you're in the mood for rowdy and raucous, and Beaches and Cream's burgers are good, but they aren't, like, amazing, so don't go out of your way if you'll be much closer in December.
Other: Well, California Grill can't be beat, but if you're worried about the Wave being too spendy, then it's definitely out. Still, you could split stuff, and you'd have a better shot at that free dessert! In other spendy restaurant news, I don't really recommend Narcoossee's, and Citricos was just "meh" in my book.
... Sez I!!!