I'm currently where you are now - in the late phase of a purchase consideration. The scariest calculation I did was the projection of MFs at a 3.6% increase per year over the next 30-45 years. When I do that calculation, i find it more difficult to take the plunge and purchase a contract.
I am trying to justify a purchase by thinking "I'm paying today for something I'll get for the next 30 years". However, the maintenance fees just seem so high when you calculate the cost per per room per night. Of course, who knows what the cost per night will be 30 years from now. That's what makes something like this so hard for me to calculate a true 'value'.
Instead of trying to figure out if owning DVC in 30 years time will still be a good deal, what interests me is, when is the breakeven point on owning DVC. Once I'm past the breakeven point, the risk of owning DVC drops considerably. Worst case I let Disney foreclose on the contract and walk away.
You can figure your breakeven point by comparing to various other options, such as what you would normally have spent going to WDW without owning DVC (ie we use to stay in a moderate with FD), comparing to rack rates with a discount, comparing to renting points, etc.
So when I ran some numbers, it worked out to around 6 years for me to breakeven. So in year 7 if for some reason I couldn't pay the MF, I could just get rid of my contract for $0 and still have come out even or slightly ahead over not owning DVC. That was something I could live with.
So the risk that I worry about is the risk in the first 6 years of my ownership. And it is because this is the way I look at it that makes the upfront costs so important to me. Lower upfront costs means less time to hit that breakeven point.