I see a lot of discussion of the time value of money, which as someone with an economics background, I can appreciate. But another way to look at it is opportunity cost. While the time value of money may be a component of opportunity cost i.e. what could you earn with this money, or, the other way to look at is lets assume you would spend it anyway, what could you do with this money.
This is more applicable to those who will be financing in some form or another, even self-financing. I plan on taking a 5 year loan out on my 401-K which I will pay myself back the interest at 5.25%. So my risk is twofold what could I buy with the income stream used to pay back that loan of about $300 a month, and what will I miss out on by removing my cash from a potentially higher interest earning vehicle.
I hate to admit this, but the majority of the 300 a month cost will be realized by lifestyle changes, i.e. being more frugal, no more, or minimal eating out, no more $50 bottles of scotch, no more HBO except when Game of Thrones is on

. Now yes one could argue we could save that money and invest it, but the reality is we wouldnt be willing to make all these cuts if we didnt have the goal of
DVC ownership.
The 2nd risk is the loss of potential gain. And while a lot of people note an assumed gain of 8% claiming it is conservative you can look at many 5 year periods in the past where the market (S&P 500) underperformed these. Especially if you look at Compound Annual Growth Rate vs the average rate of return of 5 year periods in the past 14 years. A problem with talking about average investment returns is that there is real ambiguity about what people mean by "average". For example, if you had an investment that went up 100% one year and then came down 50% the next, you certainly wouldn't say that you had an average return of 25% = (100% - 50%)/2, because your principal is back where it started: your real annualized gain is zero.
In this example, the 25% is the simple average, or "arithmetic mean". The zero percent that you really got is the "geometric mean", also called the "annualized return", or the "CAGR" for Compound Annual Growth Rate. Here is the CAGR for the past 14 years:
1/1/00 12/31/04 = -2.37%
1/1/01 12/31/05 = 0.45%
1/1/02 12/31/06 = 6.0%
1/1/03 12/31/07 = 12.78%
1/1/04 12/31/08 = -2.31%
1/1/05 12/31/09 = 0.41%
1/1/06 12/31/10 = 2.27%
1/1/07 12/31/11 = -0.27%
1/1/06 12/31/12 = 1.63%
1/1/06 12/31/10 = 2.27%
1/1/09 12/31/13 = 17.99%
And to sum up: 1/1/00 12/31/13 = 3.55%
If you want to play with the numbers, moneychimp.com/features/market_cagr. h t m
So I think the time value of money may be over weighted, unless you can pick the 2 out of 14 year where the CAGR significantly exceeded 5.25%.
And the item that is under weighted the time value of, well
time. If you have lots of disposable income then yes you can break it down to a simple cost analysis. But for many people Id suspect you will now find a way to vacation more and spend more time with the loved ones. I know I havent been to Disney in many years, primarily because I want to stay in the deluxe resorts. With young kids ages 2 and 5, if I wait until I can afford it theyll almost be teenagers. By the same token, if I waited to have children until I could afford them well, Id probably have 1 or 0 children.
The point being if by buying resale you are able to lock yourself into an affordable annual or bi-annual vacation, when you would not be able to afford buying direct or paying for the hotel, it seems like a steal to me and my family, and I cant see the value in buying direct. Its not about what the cost is today new vs the cost resale 5 years from now; its about the cost to buy today and what that will get me today and in the future vs what buying direct will get me today and in the future. Today resale will make my limited resources go a lot farther.