Just FYI, it's almost a guarantee that Disney will extend MK's hours that week (typically, 8am-11pm/1am), to accommodate the pre-Christmas crowds, just as it has for the past several years. This means the park will most likely be opening at 8:00am, vitiating the value of your breakfast reservation as a way to get into the park "early," and forcing you to squander that first precious hour after rope drop. If I were you, I'd see about switching your breakfast reservation to 10am or so, so you can squeeze in a couple of attractions before breakfast, while the crowds are still manageable.
As far as a nice dinner in the neighborhood of the Magic Kingdom, it's a bit late to find a convenient ADR for the more popular places, but I'd suggest 'Ohana at the Polynesian (or if family-style is not your style, Kona Cafe). If money is no object and you don't have small children in your party, California Grill at the Contemporary Resort would be a special experience. If you can't get reservations for any of those, you might consider Artist Point at the Wilderness Lodge (a less-than-5-minute bus ride from the MK, but often overlooked by MK visitors as it's not on the monorail line).
Have a happy birthday!
