OK, here is my evil master plan to take over Walt Disney World
We go in August, it's hot, and the park hours are LONG. We've done all day at the parks many times, we've also done mid day breaks.
The first year we went, we tried the mid day breaks the first two days, didn't work out at all for us (we were a group of 7 that year, DW and I, our kids, and my mother and adult cousin), so the remainder of the trip, we stayed in the parks all day.
The following year, it was DW and I, and our two youngest kids, and we did all day in the park every day with no problem.
Last summer, in addition to our two youngest kids, we had one of our DD15's friends along. She didn't handle all day in the parks as well as our kids did, so several days we returned to the resort for a swim, or a nap (well, not so much on the napping, I tried to though), a little computer time, what ever, then went back to the park later in the day.
Now, here is how to plan things so that you can do EITHER at whim! I use Ridemax to make our touring plans, and LOVE it. I plug in our start time (rope drop) our meal times, shows / parades etc. then put in a wish list of rides and see what it spits out. I try to adjust each day so that we can finish our touring plan before lunch. Then, we have lunch, and have an option for the afternoon. We can either spend the afternoon in the park, shopping, watching shows, revisiting favorite attractions, what ever, OR we can go to the resort for a while, and then return to the park in time for supper, and the evening parade / fireworks.
Now I rarely do this at DHS, it is a one day park for us, and we tend to spend the whole day there to get everything in, and I don't take breaks on the AK day, since that is also a one day park for us, and the hours there are shorter. If we are going to take a mid day break, it usually happens on an MK day, or EPCOT day.
I hope this helps!