I think it's important that potential buyers of DVC get away from the notion that DVC is a good investment. It's not. It's a good vacation timeshare. You'll create great memories with family and friends. You'll have experiences that will leave a lasting impression on your kids around the joys of a family vacation in world-class theme parks. You'll be generous with your "points" (read money) in ways you would unlikely be with your cash. You'll enjoy Disney more often than you would without DVC. Your kids will reflect fondly around rope dropping the new Avatar/Slinky/Millennium Falcon ride with 10,000 fellow crazies. All great memories. All great life experiences.
But none of it reflective of a good financial investment.
In the financial sense, @deerh 's example is a perfect example of how DVC is a good $21,000 timeshare, not that it is a good $21,000 investment. One can make the argument that DVC is a great timeshare, but one can never substantiate DVC to be a great, or even good, investment.
For example, it's important to take into account that $21,000 in 1999 dollars is not equal to $21,000 in 2017 dollars. Based on the inflation rate between 1999 and 2017, $21,000 is the equivalent of about $31,000 today. The sale of that contract does not represent an $11,000 profit yield, closer to a $1,000 yield, or the equivalent of growing from $21,000 to $21,650 in 1999 dollars, assuming the purchase wasn't financed.
If this was a cash purchase, there would be the lost opportunity cost of that money invested in another vehicle as well. There are the dues paid annually, and the lost opportunity cost of those dues. And then there is the extra money spent on extra vacations a DVC member will take that deviates from their vacationing norm, pre-DVC.
When looking at savings via DVC, one can't compare hotel rack rates with DVC. The closest thing for comparison over savings would be renting points to stay in a DVC resort. (Here's a great thread on this:
https://www.disboards.com/threads/how-do-dvc-rooms-compare-to-hotel-rooms.3643054/)
Personally, I will never make the argument that DVC isn't worth it. I can still remember queuing up to ride Pirates of the Caribbean as a kid at
Disneyland; the smell of the water, the sound of the turnstiles, the candlelight glows from the restaurant lighting, and the starry sky INDOORS (mind:blown); I'm excited to share that kind magic and excitement with my son next year with Toy Story Land, and the years after that with Galaxy's Edge, Ratatouille, Tron, etc, etc. Therein lies the value of DVC.
Will you save money on all the trips you end up taking? Maybe.
Will you spend a lot more than you would without DVC? Absolutely.
DVC is great timeshare. But it's not a good financial investment.