We did a "wing it" trip several years ago. We did have a few PSs. It was really horrible. But there were six of us - which is a hard number to sit. Two would have been easier. It was early Feb - before the crowds are supposed to hit.
Now we make one sit down dinnertime reservation each day and a character breakfast. Next time I'll switch one of the dinners for an big MGM lunch before Fantasmic. We don't HAVE to go, but it does mean that we will have someplace to eat. And it adds some structure to the day.
We like to spend out evenings at Epcot, so its usually not a big deal to plan for dinner. To me, MK and AK are morning parks, Epcot is an evening park. MGM an all day park.
If you do want to wing it, my advice is to do a little pre-spoting on good counter services places that offer variety. You may get lucky and walk in to sit down, but chances are pretty good at least once you'll run into "hungry NOW, hour wait." And chicken fingers get old. There are some pretty good counter service restaurants, the trick is to know which ones offer something interesting.