Think about what you really want from the trip. When we went in 2004, with a 2 year old and an 8 year old, I was so obsessed with "getting my money's worth" that we ran ourselves ragged, and by the end of the trip we were all sick and unhappy. When we went this year (kids now 4 and 10), my definition of "getting my money's worth" was a happy, healthy family having fun together. We didn't try to cram as much activity as possible into every waking moment. We did do early openings, but we were generally done with theme parks for the day by 11:30-12:00. Lunch, pool time, hanging out together, and dinner took up the rest of the day, and we were in bed at a decent hour so we got enough sleep to happily get up and do another early opening. We had a wonderful trip, nobody got sick, and we were relaxed and happy.
I'm not saying that my definition of how to do the trip is the only or best way for every single family. What I am saying is that you should really think about how you want to feel during and after your trip, and plan your activities accordingly.
I hope you have a wonderful trip.