Well, that's hard to say. I will tell you that when we went in 12/05, we had every day planned. We had no intentions of doing more than one park in a day, but I bought the hoppers, just in case. There are at least two days where we went to a second park, even if it was just for a ride or two. I know one day my boys wanted to take Daddy to see the Narnia display and ride Star Tours again. So we rode the boat from Epcot to MGM and did those things and then rode back. Another day we rode the monorail to Epcot and rode Soarin' again, then went back to MK and finished what we wanted to do. Even though we hadn't planned on those things, I couldn't have planned for what we'd be in the mood for, when. Made for a lot of great memories we wouldn't have had, like being in the front of the monorail at sunset or the fun my boys had on the boat to MGM.
HTH
Mary