IMO,
DVC is too much money to buy at a resort you may not enjoy as much as another one, if there is one topping the list. Yes, RIV has resale restrictions to it. But, if it is where you know you would enjoy staying, does your concern outweigh spending this money to then find out that staying there is difficult? How disappointed will you be? Resale locks you out of it completely.
As already mentioned, it is holding up fairly well given they are so restricted. We own both direct and resale RIV because we love it. TBH, we have never used the resale value as part of the equation because in the end, we wanted to have points at resorts that made us happy when we used them.
Regardless of the resort you buy, there is no telling what the resale market will do. Right now, Poly and VGF are doing okay, but if the new Poly tower comes out as the 17th DVC resort that is restricted via resale, any current Poly points could go down in price.
If it were me, I'd go VGF or RIV direct and call it a day. With RIV, you will get 2021 UY points if you buy a June, Aug, Sept, Oct, or Dec UY but all points with VGF start with 2022 UY points.
In the end, what is the worst case situation? You have to sell the contract sooner than you planned...life does happen...and you end up with less than you bought it for. Since dues are not the issue, if the worst case happens, chances are you will have more important things to be worried about than the potential loss you may...or may not...get with owning RIV.
Buy where you will be happy...if there is more than one resort and the only drawback for RIV is resale restrictions, but the others pull your heartstrings just as strongly, then I agree you may want to hedge your bets.
Personally, I think as more DVC come into play, and if DVD continues resale restrictions, it will become the norm and not the exception, which could keep the floor from falling out.
ETA: And, what if the unthinkable happens....DVD decides to change course with resale restrictions, doesn't put them in place anymore, and removes them from RIV. How would that make you feel?