Disney Anna:
It is such a multifactorial decision, that the economics are often not clear.
To highlight what others have posted.
We go more often now, so we definately spend more than if we were paying for a 'Disney Vacation'. A 'Disney Vacation' would only happen every few years due to the costs. A DVC stay (for us) occurs at least 3 times per year!
We treat Family Members, (or get larger accomidations) so we are not 'maximizing value'. But we are 'maximizing enjoyment'.
Because of the extra time we spend at WDW, we research, and plan and study our options, we try many of the 'special' (and expensive) offerings found at The World.
It is definately an investment in 'us'. Our vacays are more frequent and definately more fun. Including 'intangibles like, "Welcome Home", owning a piece of Disney, sneaking 14 into a studio and reusing resort mugs. (Okay, Okay, I was kidding about the last two!).
For my family and many here at the DIS, DVC is the right choice, but never a black & white, no matter how we try to break it down.
I hope it is the right choice for you too, and that we will soon be saying, Welcome Home Neighboor!
-Tony