DVC is a great option if you vacation regularly... And you don't have to vacation Disney all the time, there are a ton of DVC, non-disney places to go... Skiing, Spas, etc... all over the US and overseas!
It's not like time-share where you are locked into a set location. You select a "home" and your "dues" pay for the upkeep of that location. But your points are good anywhere. At certain times of the year you might use less points for a stay, just depends on what season it is, etc. SO if you are willing to travel during off season you can really get some good deals.
the 15-20k is a good ballpark range for the basic points. But you are figuring that is over 40 years, and financing is available. You have the normal dues and fee's that come with timeshare, but like I said, there really is a lot of flexibility to where and when you go.
Anyway, if you are planning a trip to WDW, definitely stop by a kiosk, or go to the Sales office at the Boardwalk and sign up for a tour of some of the venues... and the new Saratoga (ex-Disney Institute) DVC resort sounds WONDERFUL, it should be ready in the next two years I imagine...
Hope that gives you a better idea.
