I've found that for most people, but especially kids, the anticipation leading up to something is a sizable part of the fun. If you have an exciting vacation coming up, take every chance to remind your kids that it's coming, what the plans are, etc. If you don't, they've missed out on half the fun!
I'm also convinced that this is why so many people can go to the Disney parks. The lines are amazingly long, and the actual rides amazingly short. It's the anticipation of going on a ride that keeps you happy.