I agree that it is makes a lot of sense to buy directly from Disney when you want add on points, especially when you want the same resort and you want a specific number of points. I just added on 170 points to OKW and they came with 15 year extension. If I had tried to buy resale at around $75 I would have been restricted to whatever number of points were available and they wouldn't have had the extension. (I know there's been a lot of discussion on the extension, but it works for me, actually my grandkids).
At a resale of $75, plus the extension brings it up to $90, Disney pays for closing which probably equals about $2. point. I also get all 170 points for '07, so they're worth at least $4. each, which brings me to $96. Why hassle with resale....