I recently made my purchase to join DVC (bought AKL resale since I saved over 30 dollars a point as opposed to going through Disney). I'll be honest and say that my family spoiled me with deluxe stays over the years, and it was something that I didn't want to give up in the future. I had the money to completely pay out for the 200 points I wanted, and I figured that now I only have to worry about the dues (which will continue to be less than the cost of a similar room).
I think the major factor for people is the room vs resort argument. If you use your room as a place to sleep, then DVC isn't really for you. As Richard said, he is very content with value and moderate resorts because that works for his family. If that is your vacation preference, then DVC isn't a good value for you. After all my trips to Disney now, I find myself spending more time enjoying the ammenities of my resort. I like to relax, spend time at the pool, and take in the other offerings of the resorts. The deluxe resorts offer me things that I enjoy, so I decided that I might as well lock in on my purchase now and be able to enjoy it into my 70's if I choose. In the worst case scenario, I can always sell my property. I won't make nearly the money I spent a few years down the road, but there is always a way for me to alleviate myself from the dues if I have to.
I think another imporant factor is money management. As odd as it may seem, DVC is an emotional purchase. Disney completely recognizes this and markets it that way, which can cause some people to not think through the process. You will see a lot of people who finance big contracts and find their dreams ruined through the costs they have to pay. Each person has their own thoughts on spending their money, but I agree with many when I think that vacations are luxury items. If I wasn't able to pay outright on my contract, I wouldn't have purchased. I believe that only neccesities should be finance (car, house, school) and luxury items should be a save and buy. Of course, each person differs on this, but it is important to take it all into consideration when you are making your decision. Disney is banking on you to think with your heart and not with your head sometimes.