Hi, Jodie! I think this is really a personal preference sort of thing, and what may work best for my family may be different than what works for your family.
I will say, if you get an early reservation for Crystal Palace for breakfast, it can be almost like your family is the only one at the Magic Kingdom. I love photos taken early in the morning, when there is no one standing behind your family as you get that picture in front of Cinderella Castle. It's almost like you have the whole place to yourself!
My family, however, is not big on breakfast. At home, I'm lucky I can get my girls to eat a bowl of cereal or some toast. Even on the dining plan, I can't see the value for us in breakfast, since the kids will probably only eat a few bites of something. They seem to have an aversion to big, hot breakfasts unless their Pop-Pop is making it for them.
I would much rather spend a few dollars more and have lunch, knowing that at least I can be assured that the children will actually eat something. The choices at both breakfast and lunch are wonderful and varied, but I know my kids would do much better with some salad, mac and cheese, and a nice dessert than they will with eggs and bacon.
I personally don't prefer one meal over the other - the Crystal Palace breakfast is equally as delicious as the lunch. But for us, lunch is the better value.
Have a great vacation!