Some good advice here already, but I'll also chime in that you can get a good, filling, non-burger meal in any park at a variety of counter service places. This does away with the ADR dilemma and and preserves the flexibility you're concerned about. A few examples of my favorite "real meals" available at CS places include:
Columbia Harbour House in MK (shrimp platter with steamed broccoli and coleslaw)
Tangerine Cafe in Epcot (lamb and chicken shawarma platter with tabbouleh, hummus and couscous)
Flame Tree BBQ (1/2 chicken with baked beans and coleslaw)
And those are just a few examples--there are many others.