I love Shamus' financial analysis, but the point that is easy to miss here is that the DVC resale marketplace is not a free market system. It is a marketplace with an elephant in the middle of the room setting the resale prices. The elephant in the middle of the room is Disney, through their exercise of their Right of First Refusal (ROFR)
Disney does several things with ROFR, but I'm sure the main purpose of ROFR is to prop up their direct sale prices. If they did not ROFR, and instead allowed resale prices seek their own level, a larger gap would emerge between direct purchases from Disney and resale. Eventually, the gap would get so wide nobody would buy from Disney at all -- they'd just buy resale and save money. Why would you buy SSR for $90 if you could get BCV for $40?
Prices for sold-out resorts have risen as several posters have mentioned, and someone who bought in 10-12 years ago is indeed in a position to make a nice profit today. But why? Is it that the value of the rooms has risen? They have but I don't think that is the reason.
The reason for the rise in resale prices is that a resale buyer has two hurdles to clear, not one. They first have to make an offer the seller will agree to, but they also have to place that offer high enough that Disney will waive ROFR. If you read Beca's thread on the DVC Community Board, you will see a number of situations where buyers either paid more than the asking price for the contract, or they went back to the seller after agreeing and asked, "Could you please let us pay a little more?" The reason, and the only reason that happens, is the buyers are worried about the elephant in the middle of the room snatching up their contract. ROFR is the floor of the resale market - not the intrinsic value of the contracts.
If Disney ever decides not to ROFR any more - for whatever reason, and I could give you several - the resale marketplace will change radically. It seems to me that DVC would remain more valuable than traditional timeshares, just because of where it is, but I think the prices would be considerably lower than they are now.
As CarloMN and others have suggested, I view DVC as a vacation opportunity, not a financial investment.