DVC has different sales promotions through the year. Tickets, bonus points, discounts (if you give up current year's points), "free" vacations, have all been offered in the past but they are across the board and open to the public at the same time (presales maybe offered to current members) and once the promotion is over, it's over.
Pricewise, it seems that the current 15% off is one of the most generous promotional incentives ever and you won't have to give back or sell back your current year's points to get it. The promotion ends 2/1/06, I think.
If you are asking if there are any "hidden" discounts that you are unaware of that you can currently take advantage of, then no, there isn't.
DVC may offer "free" vacations, tickets, bonus points, or even discounts after this current promotion but keep in mind that the price per point is steadily raising so you may wait for a "better" promotion but wind up paying more.
Good luck with your decision.