i think the most important thing is like another poster said... knowing which ride to go to at which time of day. our first trip to wdw w/ the kids (4 years ago), we wandered from one end of magic kingdom to the other, hardly rode anything because we wouldn't wait on a line longer than 20 minutes, and had a horrible day. i thought i had everything well planned. but i had only planned which parks for which days and meal ressies. i had no touring plan. For our next trip, i knew (and researched what i didn't know) which rides to hit first thing in the morning, which to grab a fast pass for, which ones could wait till later in the day, etc.
We never wait more than 10 minutes for any ride now, and we go on everything multiple times each trip. we also go during busy times (easter week, 4th of july week, columbus day weekend). I've never used an actual tour plan from a book, but i'm sure they're great.
here's a quick example... for magic kingdom days, we'll get there for morning extra magic hour and do all of fantasyland, adventureland and frontierland. then around 10am-ish (remember, we're going during busy times - we've been to MK when it opened at 7am and done all those lands multiple times by 10am - we walked on splash mountain 5x's in a row before it got a line of a 15 minute wait). But even if it opened at 9am, you'll have at least gone on everything in those lands once by 11am... then we head over to tomorrowland and grab a fast pass (we usually grab a buzz fast pass, but you'd probably want a space mountain fast pass - i think your kids were older), then eat something and do carousel of progress, tta (both are usually walk-ons), watch a show somewhere, shop or pin trade till our fast pass time comes. and remember you can grab another fast pass before your time comes for your first one. it tells you on the fast pass when you can get another one. so grab another one, ride your first fast pass ride, then while waiting for the next fast pass ride, do other stuff (mickey's toon town, swiss family tree house, tom sawyer's island, small world - all stuff you usually don't have to wait in line too long for... don't do these during precious morning hours - save them for waiting between fast pass times).
you'll have done everything 'important' by early afternoon, and can 'relax' the rest of the day (eating, shopping, pin trading, doing shows, fast passing, doing rides w/ short waits, really checking out everything in the park you'd miss if you were rushing through it. sometimes we'd have early lunch ressies
(11:30am), be done w/ everything by then, eat, and leave the park for swimming (just as the crowds were swarming in)... we felt very satisfied that we had done everything we wanted. we'd then come back later for parades, etc.
hope that helps! you can't overplan a disney trip... just keep in mind your plans can change and just be flexible.
enjoy your trip!