Although
DVC Mike's list is correct that the price per point is higher buying direct, it is possible that the total cost for the points you get the right to use will actuallly be less. The reason is that DVC never sells a contract which has been "stripped" of current years points, but many sold at re-sale are stripped.
In addition, if you buy from DVC before the start of your UY, you will get an extra year's points, but pay no more in purchase price and little or nothing more in MF. So, when we bought our Aug UY in April in 2005, we got 2004 and 2005 points. We paid MF for 2/3 of the year, from April thru Dec.
As a result, if you can find a "fully loaded" resale contract, the lower price per point will save you money. However, if all you can find are 'stripped" resale contracts, you should do the math to see if the price per point is low enough to make up for the loss of one (or more) years worth of points.
Best of luck -- Suzanne