For me it's really a how much am I spending on dues vs rack rates w/ discounts. If the spread isnt big enough than I am no longer comfortable. If dues rise to $18 per point but reservations are equivalent to $25 per point in cash then I would be uncomfortable and look to exit.
I think this is the way to look at it. I think a quick proxy is what are the major brokers willing to pay you to rent your points. Right now, it's probably $16-$18 per point, and then they rent it for about $25 per point, give or take. And, they can do that because the cash rate is well above that, so if you rent through them, you're getting a big discount. If dues start to get close to (looking at you, VB) or exceed the amount you can rent your points through a major third party broker, we're approaching problem territory.
That said, as I type this from my RIV balcony with a view of the MK fireworks (saw Epcot earlier in the French pavilion), the one thing I am reminded of every time I come to the House of Mouse, it is just how much worldwide appeal this place has. Whether it was visiting each waterpark, MK, Disney Springs, or Epcot, I don't think the appeal of a deluxe DW resort is going anywhere anytime soon. Of course, none of us know what the future holds, but DW is as close as one can get to an American icon. By some accounts, the MK is the most visited tourist attraction in the world. No,
DVC is not an investment, but I think one could make the case that, when kept for a long enough period of time, even with the resale restrictions, it is close to being a stable cash asset.
Ok, back to my glass of wine with sprinkle of pixie dust

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