Given where the parks are now, I understand why Epcot and AK should be the first priorities. Epcot's attendance is sinking like Stitch in the Pacific Ocean, and AK has declined each year since it opened.
But all the parks need a certain amount of ongoing investment, and I'm not sure that one major attraction every 8-10 years is adequate (3-4 years since RnRC, +5 possibly until next). Perhaps things like Cinemagique, or a replacement for Hunchback will tide MGM over, if they do happen. But if MGM really is largely ignored for another 5 years, Disney may find it in the same shape Epcot is in today, and need another "revitalization" (Eisner's word, not mine).
You can't rob Peter to pay Paul and expect Peter not to suffer.
For us, MGM is a day and a half. We have a 4 year old, which brings Playhouse Disney into the equation (for now), and some of our group enjoys ToT and RnRC, though we don't like that we have to split up due to some not being able to, or not wanting to ride.
That said, we were underwhelmed by the backlot tour, and skipped it last time. Millionaire has no appeal to us either. With Hunchback now closed, and the GMR probably going to be closed for rehab on our next trip, MGM probably is back to a one-day park for us. Due to Star Wars Weekends, however, we are scheduling 2 days...