I agree with Dean, which is why after years of running numbers (I'm an accountant and process analyst - and currently a trophy wife), I've come down on the side of running the numbers is fun - but its fairly meaningless - because the assumptions are all over the place and it is the changes to behavior that really increase the cost. And because - risk. When the economy was good in 2006-2007, we saw a lot of people buy
DVC using this sort of math and assumptions that didn't prove out when the economy got worse - some of those people lost their shirts on DVC - some of them lost their homes. I'll never again tell someone DVC will save them money - it sure didn't save people who bought in 2008 and sold at a loss in 2009 any money. The assumption there - you can resell it for what you bought it for - and you won't anyway because you'll be going to Disney for at least ten years - didn't pan out for those people.
Dean and I disagree on one point - he thinks it needs to make some financial sense. I think that if you have enough money, it doesn't need to make any sense at all. I used this example last week - I drive a Prius. I probably don't save money on gas over buying a Jetta diesel - not enough to pay for the difference in the price of the car - but its an affordable loss and I like my Prius - even though it has hamsters for an engine and a huge blind spot out the back window. My husband wants a Tesla - and not one of the next year affordable sedans - he wants an S. While we'd save on gas, his Mercedes is going to come out much cheaper to own than the S - and we CAN'T afford that delta - not without dipping into the kid's college money. But I have a friend with an S - apparently financial sense did not enter into the equation - he wanted, and can afford, an S. Neither car really makes financial sense (neither does the Mercedes), but you should drive something you enjoy - and you can afford.
To me, it comes down to "is DVC a good fit for you" (the onsite, no housekeeping, make plans in advance, be able to get multiple room units, like the resorts, etc. attributes) - and "can you afford to burn the money - or at least a significant amount of it - because if the economy crashes next week, you might be doing pretty much that."
And almost no one asking if DVC saves them money over a regular resort room, or asking for the math, meets the second criteria. When they come asking if DVC is a good fit - it might be.