When I bought my WKV week I also considered that the value would be zero at 10 years. That was a fairly common theme on TUG back then and very few of us at the time thought the weeks would be worth close to the purchase price. On the other hand, IIRC very few would suggest that WKORV (which at the time was ~$35k for annual OV resale) would be ~$10-12k in 15 years.
I paid $20,500 for my WKV Platinum in September 2005. At the time it was a very good price, though not exceptional (it was akin to the ~$14-15k price today, not the rare yet always mentioned and hoped for $10-12k price). So in 14 years, the value has reduced about $5500-6500, or about 29%. During that time we went through both economic growth and worse. Assuming it loses another ~30% in the next 14 years, then a value of ~$14k would be $9800. Based on this I find it very difficult indeed to agree that it will be valued at zero in 10 years. We are no longer shooting in the dark as we once were...we have historical perspective to help balance our opinion. So, while it may be smart to still consider any timeshare worth zero the moment after purchase and intend to use it for 10+ years to redeem your value, the reality seems to favor that good timeshares will retain value.
It sounds like you're convincing yourself to buy conservatively, which I think is smart. Telling yourself the weeks you own are worthless is a great way to find solutions to using what you own, and if it has any value at all in 10 years you'll be happy.
Of course, I think you're overly pessimistic about the eventual value of the weeks (depending on resort). Just remember that there are a lot of timeshares out there, and they also trade in II for VSN/Marriott. I highly doubt that II will suddenly dry up with VSN/Marriott weeks for others to reserve, so even if the worst happens and the VSN club is killed and we only own the resort itself with trading in II (this assumes no overlay), then I think we will *still* be able to trade to nice resorts. And this won't happen.