There is a lot of great information on the boards about
DVC and what it has to offer.
It is a great program for those that like to visit WDW on regular basis, who want to stay in bigger rooms, and those that can plan vacations far in advance.
You buy points at one of the resorts and this becomes your "home". You get to book reservations here whenever you want, providing there is availability when you call--that is the reason for needing to plan vacations well in advance.
When you go, which resort you pick, the room size, and the number of days, will determine how many points you need for your travel needs.
As far as investment, do not buy it for that reason. While those that bought in when DVC first began (early 90's) are still seeing a good value for their contracts on the resale market, there is no guarantee that this will happen.
We bought in to BLT last year because we wanted to commit ourselves to
Disney vacations for many years. We knew that over the course of time, what we were paying to join DVC, initial cost and yearly MF's, would be less than just paying cash.
Basically, after 7 years or so, we will be getting our yearly summer trip of 5 to 6 nights in a 1 bedroom for less than what we had been spending for the same trip to the CR in a regular hotel room.
Ask lots of questions and research before making anyway decisions!
Good luck!