What we did last year, and are going to do again in July is this..
We drive down from St. Louis, which is about a 16 hour drive. Last year we planned on stopping around Valdosta, GA to sleep for the night. We just figured we would see how far we got, and then get a cheap hotel in whatever town we were in. Well, once we got to Valdosta and it was only 4PM, we just kept on going. Around the Florida state line, we called WDW and just asked for a value room for the evening. We had a 7-night package at POP, but we stayed the first night at ASSp. It was fun, because the kids got to see a totally different hotel, and got to swim that first night in a totally different pool. They still talk about it!
We plan on doing the same this year. We have our 8-night package at POP again, but are just going to call and get a room at any value the day we drive down! That way there is still a little excitement on the way!
Also, we get up early the next morning and check into POP first thing. We got a really nice room last time that way..