This is what I thought when I bought, but now I see a lot more risk, and it's coming from inside the house.
There are a few more paths I can imagine, like saturation. Direct becoming a motivated seller and knocking down the price could devalue points, like VGF2 did to VGF1. Right now,
DVC isn't selling enough points to cover what it is introducing into the system, and that's before VDH and Poly2. DVC is holding a lot of bags and still building.
Another path would be hostility to renting points. A whole lot of DVC is controlled by professionals. If Disney starts messing with them, they are going to have to sell, which would move the market. I don't think they will do that, as Disney would rather have families from Denver than timeshare cheap-os, and DVC doesn't care if someone is paying the dues. But who knows?
And then there's the park decisions... So much uncertainty here. Who knows what wild choices the parks could make in the future. They could be good for families from Denver, but not for DVC.