chalee94 scenario looks reasonable to me.
Another way to look at it, assuming you (or family, etc.) use the whole life of the contract:
I see some current listings @ TTS for as little as $80pp, but also several @ $83 - $90, so $85 sounds like a good price.
250 x $85 = $21,250.00
Let's assume you get first points & trip in 2010 and start paying dues then, seller pays closing just for the sake of argument. Also, I'm going to assume dues go up 4% every year, meaning in 2041 (the last year I think you'd get points) they would be ~$17.54 per point, or $4,385.69.
So, for the 32 years of points in my calculation, total dues are $81,523.32, for a grand total cost of $102,773.32.
Now, I think it is safe to assume renting points will always cost AT LEAST as much as dues for that year, and probably won't drop below the $11 you paid since cash ressies will almost certainly go up. Using that standard (which I think is unrealistically low for the rentals), and only 238 rental points so this isn't apples to apples, you would lose $7,469.70 by buying because rentals would end up being $95,303.62.
If we assume the rental price will be the greater of $11 or 21% more than actual dues, then I get the rental going from $11 through 2024 and then slowly climbing to ~$21.22 in 2041. That would total $103,188.90 in rental fees, so you'd save $415.58 by buying.
Now let's say that the rental price goes up at the same percentage rate as dues every year (which might keep pace with half the price of a cash ressie from CRO for example), sticking with 4%. That would then work out to $11.44 through $38.59 per point rental, total $170,718.54, and by buying you'd save $67,945.22. I think this is PROBABLY the most likely type of scenario.
Finally, let's say dues and the rental price stay perfectly flat [almost guaranteed not to happen, but for the sake of argument...] You are then looking at $83,776.00 for the rentals vs. $40,005.60 in dues for a resale total of $61,255.60, thus saving you $22,520.40.
SOOOOOOO, it really depends a LOT on what you think the future rental market will be like relative to costs of owning. I think that most likely you would save money (possibly a LOT) in the long run by buying assuming you or your family will continue to use it, but that certainly can't be guaranteed...
Hope that helps!
PS- I am admittedly leaving out the "time-value-of-money rate" type of arguments because then you can really get your head to spin, but I will acknowledge it as a valid factor for some, especially when paying cash for the up front purchase. If you finance I think that becomes less of a factor.