One thing I might suggest is to always figure in some flexibility in your schedule. The reason I say this is because when I was down there for 4 days, I had to try 3 times for Spaceship Earth (it was broken down for a few hours one afternoon). I ended up getting on SSE two days later, instead.
Another day, I had planned to hop on the monorail from MK over to Epcot. The monorail had broken down while I was in MK. So I ended up waiting for a bus to my hotel (Swan), and then I had to switch over to a Friendship Boat (they go between Epcot and DHS, with stops at the Beach Club, Boardwalk, and Swan/Dolphin), to get to the back entrance (International Gateway) of Epcot, for the evening.
Neither one of these breakdowns was extreme in my case, but for those guests who really do plan out everything for each and every day, I worry a bit for them. (Hypothetically, let's say I had an ADR over in Epcot, and the monorail from MK to Epcot was down. There's no way I'd make the dinner reservation on time, unless I took a taxi from MK.)