Be careful about "getting your money's worth." When you start thinking that way, you push to ride "just one more thing" about four or five times, tire yourself out, stress yourself out, and the kids too. This happens even with the best of intentions, which you clearly have, and good for you!
I used to be a "get my money's worth" guy until I bought a season pass at Cedar Point, my homepark---since each admission was pre-paid, and I could come back some other time, I started taking a much more relaxed approach---I didn't push to get in "just one more ride", and I didn't wait in lines I knew would be shorter some other time. And, much to my surprise (I guess I'm not all that smart) the relaxed approach was a whole lot more fun. Now, I follow that apporach every time our family visits any park, even if we are visiting on full freight single-day tickets.
Our standard theme park days look like this: arrive at opening or a bit before (my kids are early risers), tour until about 1 or so (including a quick counter service lunch), go to hotel to rest/nap, come back for a handful of short-wait attractions (at most) and a nice dinner, or maybe a show, or just to enjoy nights in the parks. We're heading back to the hotel by 8; 8:30 at the latest.
If we are only visiting a park for one day, and aren't staying nearby, we come in at opening and stay until about 3 or so, and then we are out of there.
We've been following this model for the past three years, both at our homepark and parks we visit elsewhere, and my kids are 4 and 6 now---they are starting to get old enough to stay up a bit later, and maybe not nap every day, but we still get out of the parks every day in the early afternoon without fail.
This is a plenty full and fun day. If you are there at opening and leave at 1, you'll probably see more attractions than you would if you arrived later and stayed through until the kids collapse.
We even did this at
Disneyland last February, where the parks open an hour later (10 rather than 9), and we were staying offsite (at least 30 minutes from hotel room to front gates, so 2 hours a day communiting to and fro) and STILL had a great time and plenty of fun. You might need to spend an extra 15 minutes each way at WDW, but the parks open earlier, so it's a wash.
True, some families with similarly-aged kids happily and healthily spend more time in the parks when they visit. As far as I know, we could do it too with no ill effects. But, I have found I am getting more than my money's worth out of this plan. The way I see it, time spent laughing and playing with my spouse and kids are what I'm paying for---the parks and their attractions are just the stage on which we play.
Edit: I will add, though, that my plan absolutely requires either two connectiong hotel rooms or an honest-to-goodness suite with at least one private bedroom. That way, DW and I don't have to pretend to be asleep in a darkened hotel room during nap time and bed time.