We wouldn't skip any of the parks for several reasons. I don't actively dislike any of the park attractions that I can think of; I may not LOVE some of them, but I'd rather be at WDW than doing most other things. I would hate to travel so far and skip any of the parks. (Note that we always get park hoppers, so we aren't ever married to spending an entire day at any one park.)
My immediate family and I had been going to WDW approximately yearly up until a couple years ago (we've skipped a couple years because we had so much going on - new baby, moving across country...). So besides never having been able to do "everything" there is available to do on WDW property (or even just in the parks), several things are new since we were last at WDW (notably BOG, 7DMT, and A&E). There are several other things that we've never gotten around to (such as Jedi Training Academy), or that we've only done or seen once (Animation Academy, Flights of Wonder, LMA, Indiana Jones, TSMM,...). There are also many more things outside the parks that we've never done (Typhoon Lagoon, mini golf, either of the dinner shows,...).
My parents and brother are also coming along this time (they've each only been to WDW twice, most recently about 6 years ago). There are many rides and attractions that my parents and brother have never experienced. (DB has never been in the Enchanted Tiki Room; hasn't ridden Dumbo since he was a small child; I don't think he's ever been to Tom Sawyer Island; never seen Lights, Motors, Action; never seen any of the shows (FOTLK, Nemo, BatB); I don't think he's ever even seen Fantasmic!) We're looking forward to introducing my parents and brother to some of these new-to-them ride and attractions.
Especially for those of us with small children, each trip is different because the kids are physically and mentally able to do more and more each trip. DD is petite for her age, and she is finally tall enough to ride most of the 'thrill' rides at WDW (this will also be DS's first ever trip to WDW). Even if DH and and I have experienced something a hundred times, each time we ride or see something with one of our kids for the first time, seeing it through their eyes makes it like a whole new experience.