I think most timeshares have zero or very little value, as the maintenance fees have escalated to the point where most weeks can be rented for less than the annual maintenance fee or very close to it.
The only value if it is already owned is the convenience of having the week.
I can only speak about Marriott owned timeshares and rental returns in relation to maintenance fees (initial purchase cost is ignored). - My experience with Marriott owned weeks does not support Vail's generalization. At the buy, it's pretty easy to determine the rental market by resort & season by simply looking at rental listings (by season) and maintenance fees. Some are worth owning for use and the rents are fine. Look at Newport Coast platinum season weeks as a pretty good property. I will not mention some I consider dogs but it's not hard to isolate them. Of course, no one should buy an owned week strictly for the rental income but should buy the property because they like to go there.
Purchased points are an entirely different animal and I have not experienced even reasonable returns compared to the $.70 maintenance fees. Mere recovery of the maintenance fees is the more likely outcome. Good reservations for use or rental are just too hard to get - lots of points are pointed at the best reservations. I have difficulty with MVC's efforts to stop rentals as I think they are likely exaggerating the impacts and hurting those stuck with small numbers of near un-spendable points. I wish they would share some specifics of one of these culprits so I could see if these activities are as dumb as I suspect.
It might be that MVC's real target is those who exchange their enrolled weeks for points, make point reservations, and then rent them out. The maintenance fees on these points are much lower than those for purchased points. I suspect MVC is even surprised by some of the outcomes and challenges of this points program.
Only my view.....