We really liked Kona Cafe (fabulous desserts) and The Wave (also fabulous desserts) Both are on the monorail, so convenient to hop to parks from there too. And they're a little easier to get reservations to. Very good steaks at both places if you're looking for a really special meal.
For excellent buffett, Crystal Palace in the Magic Kingdom.
Have you ever eaten in the castle? It is 2 TS credits apiece, but really is an awesome place to eat. Some people don't like the food, but we thought the prime rib was good. And anyway, it is just a great experience. They do have an elevator for those who cannot do the steps.
I would not bother ordering a special cake (and they're not cheap, either.) You'll just end up with way too much dessert, and then what do you do with it after you eat (you don't want to carry 1/2 a cake around a park the rest of the night!)
On the
DDP you would still get the dessert that comes with the meal...we were always so full from the meals we never even could finish the desserts (which were all wonderful at every restaurant we've tried.)