I second the idea of doing buffets as often as possible. It's hard to find individual restaurants that have something that appeals to everyone and buffets relieve much of that guesswork.
Ohana's isn't actually buffet - it's all-you-can-eat served family-style (the food is brought to you and after a first pass they'll keep bringing whatever you want) but I always enjoy it.
Boma is a must-do on all of our trips. Jiko would be great for an upscale night or a special night like a birthday. And speaking of brithdays, you CAN order ahead and have a birthday cake waiting. Not sure if 407 WDW DINE is the number to call, but if not they'd be able to give you the number to call for Special Orders.
Finally, you might want to consider some of the restaurants in out-of-the-way resorts, if only because it'll probably be easier to seat large parties in 'em (granted, I could be wrong about that on any given night). I"m thinking Olivia's at OKW or Turf Club at Saratoga, maybe Boatwright's @ PO-R though that tends to be quite popular because the resort is so damn big and gets runoff from POFQ, too.
If you wanted to use 2 table credits for a Signature Dining Experience, I always recommend balancing it out with the buffet at Fort Wilderness. THe food isn't awesome, but it's pretty darn good, and the price is the closest thing to a "value" you'll find anywhere for a full meal in WDW
Pay for that out of pocket, and you have the extra credit for the fancy meal.