Thanks for sharing your thoughts. I agree on a few things and disagree on a few others, and figured I'd share the highlights below.
At the time, I put together a good spreadsheet comparing the options, with present day value and future investments for the cash needed, the time required to save for it, and other factors (need to see if I can dig that up, but the spreadsheet may have gone the way of the dinosaurs). In all, I came the following conclusions:
1) the average break even point for financing would be about 30 years; about high 20 years compared to Value resorts, and Moderates were in the high 30 year mark. Deluxe were down the tubes (slightly above by a couple years), but I knew we'd never stay at a deluxe with regularity on cash.
I was surprised that given your background and after doing a pretty sophisticated financial analysis that you still decided to go ahead with a financed purchase, knowing what you knew.
2) the
premium we pay for financing is the price for the
intangible value we received from owning
DVC by buying in early.
This is where Ken's numbers shine. How much are the memories worth? His numbers provide a tangible cost for some to determine if the anticipated emotions are worth the price, or would delaying these memories (or collecting them elsewhere) be better.
Ok, now I'm less surprised. While I disagree with this type of thinking, I'm not about to say that you're wrong. Because who knows, maybe I'm the one that's wrong here. But my different thinking is that owning DVC (or even renting it for that matter) is not necessary to have wonderful family vacations at WDW. Sure the accommodations are fantastic, but there are many, many other ways to have a great stay at Disney without DVC. But at least you are accurately identifying the missing portion of the equation. Owning brings you happiness. Happiness comes at a cost.
For us, the memories we have made are worth the additional expense, already. Plus, we've garnered good will with friends and family that have vacationed with us or we have put up on their own vacation. In the end, the additional cost was a good value, and the value continues to mount.
See this is where you and I differ. You are generous and I am clearly a cheap (insert appropriate noun here).

Family might be a different story, depending on how close we were, but I would not let friends stay in my DVC accommodations for free. I recently went on a trip with a good friend's family and even then I charged him a reasonable fee ($10pp for BLT points). So yeah, I gave him a bit of a discount, but I would not go so far as to let him stay for free, just as I would not pay his room charge if we stayed in a conventional hotel. Furthermore, I certainly would not do this if I still had a loan balance on my DVC contract. So while what you did was incredibly nice, it's the equivalent of taking out a loan to buy your friends dinner. Doesn't seem like a great financial move to me. That being said, your friends probably like you more than my friends like me.
Now, for my perspective on some comments...
...As for the future income stream, this was a point my DW and I discussed; who do we want to receive the financing money (if we did finance)? In the end, we decided giving the interest to Disney would serve our personal short and long-term interests as any additional cash in their pockets might help make them profitable and remain, instead of close shop and take our DVC with them. While I know we won't effect Disney on a grand scale (they aren't waiting with baited breath for our payments), if we had to pay someone interest, better to go to Disney (we thought).
This is not the first time I've read this type of thinking and I always find it fascinating. Disney does not care one iota about you or your family, so I am curious why you care about them. You make it sound like enlightened self interest (keep DVC in business so that you can continue to stay there) but in my opinion, that is not your responsibility or concern. Plenty of people get paid plenty of money to insure that happens. (Or sometimes they get fired because they're not insuring that it happens).
Sometimes it is better to sit on the cash and finance instead of pay cash for an item, and successful businesses do this all the time.
I agree with this with one very important caveat. You can't just sit on the cash, you need to be able to put it to work for you in a way that earns you more than what you would pay in finance charges. If you don't (and many, many people don't) then it's just a theoretical argument that does not apply.
As for the idea of over committing without being able to repay, I don't think many in this nation saw the recession on the horizon, despite ample warning. I would think most who finance are employed with a stable job, and they did (do) not anticipate being terminated. Also, I do not think DVD would let those in serious danger of over committing get financing; however if they do, the foreclosures are calculated into the loan's risk analysis.
But that's just the thing...people don't see this coming and they get destroyed when it happens. At some point you have to have a little foresight. Nobody anticipates losing their jobs, but if they were wise they would be prepared.
As for DVD not letting those in serious danger of over committing get financing, I disagree with that assessment. The two major criteria on being able to get financing with DVC are whether or not you can make the down payment and whether or not you have defaulted with DVD before. If the answers are yes and no respectively, you'll get your financing. Although like you said, that's where the 17.5% interest rate comes into play.