We have been all over the map on this, and I entirely agree with Mickeynut's advice to play it by ear. We have three kids (our oldest is almost 17 now) and we've been taking them to Disney since they were tiny.
Our older two always functioned best if they would go all day, have an early dinner and then call it a night around 8pm. I honestly can't recall a time when either was crabby or overtired - except when I tried to take an afternoon break with our oldest! I read so much advice about the afternoon break, so I tried that with him when he was two years old. It was a disaster. He was a stroller napper, but could not fall asleep in a hotel room. The whole bus back to the resort, try to sleep in the room / rest routine didn't work for him. The forced break was stressful for all of us. He needed that stroller nap, and I enjoyed quiet time in the parks strolling with him. So the day we missed out on that, we were both kind of crabby.
Our youngest is completely different. He absolutely needs the afternoon break, so we go with that. As a result, we're usually in the parks in the morning, resort break after lunch, then back to a park (usually Epcot) for dinner.
So I can't say there is a right or wrong answer to the afternoon break question, and there is a good bit of trial and error. It continues to evolve for us!