I'm another that, when I can get my butt up out of bed, and find the "EMH-park early, then skip to another park" technique to be very effective, mostly at MK and MGM. At the MK it's the best to go from there to Epcot, since it's just a nice monorail ride and they tend to run more quickly than the busses.
I was just having this conversation with a close friend of mine. She and I visited WDW seperately last October and couldn't have had a different experience. She and her husband said it was too hot, too busy, and they didn't spend many days in the parks because of it. I had the opposite time - it was hot, but at mid-day when it was worst we found something indoors to do, or took a long lunch in the cool air conditioning.
The biggest difference was our experience in the lines. They arrived every day at 10:30 or 11 with the mass of other late sleepers. By that time, I've seen half the park and am in the back sections, where it's still relatively empty while the mass of people just coming in are just experiencing their first attractions at the front of the park.
If you can manage to get up early enough, you can see the major attractions in the MK (Buzz, Space, Fantasyland dark rides, Haunted Mansion, Splash, Jungle Cruise, Pirates) before 11am, just in time to head out as the throngs of people who planned on that day at the MK because of EMH but didn't get up early enough and came anyway, are arriving. Then have a casual lunch somewhere - the counter service at the Contemporary and the GF isn't bad, or you could opt for a more extravagant sit-down lunch, and then head off for the afternoon at another park.
That works very well for us. If you have younger kids, then going back to the resort for a rest can be very beneficial, but with teens/adults we don't find it necessary if we take a long rest around lunch while everyone else is running around in the hottest part of the day doing the attractions we already have done.
NewEnglandDisney