We've gone to WDW in October / November for several years and love it. As long as you avoid the holidays, the parks are very uncrowded and only the most popular attractions have any significant wait. Hotel rates (or DVC points) are lower then, too. We've even checked in on the Sunday after Thanksgiving, and while there was some hustle and bustle, by late afternoon things had mostly calmed down.
In October you stand a good chance of having a nice warm day if you wanted to go to one of the water parks. On the other hand, the first week of December is notorious for being chilly (and this year, downright cold).
That said, you'll still need to do a little planning - restaurant reservations fill up quickly, and MK can still be a little crowded on the weekend or late in the afternoon if the weather is nice.
We've stopping shelling out the bucks for
MNSSHP and
MVMCP, but you can still see Main Street decorated for the holidays, and starting in early November, you can catch the Osborne lights.