Buying resale gets you the deed to the points, for the length of the deed. As mentioned above, the length can vary by resort, or even within resort (OKW, I'm looking at you). Everything beyond that (I believe) is a benefit that is provided to you by DVC as a perk of owning, and not as being included in the deed. So as mentioned, the ability to use your points outside of DVC resorts, they were able to not offer that to points purchased through resale. But they had the right to still offer that to new points bought from DVC directly. This does in theory give them the right to take away other perks that all members currently enjoy such as AP discounts, dining discounts, etc. But as of now, those are still extended to all owners. The only difference between resale and direct are the limitations on the different ways you can sue the points.
When you are looking, you will need to look at all the details. Most resales will include the per point asking price, the use month, available/coming points, and paid/owed dues. Some transactions will include points that the owner banked last year, (loaded) while others are sold after the owner already used this years points (stripped). Some owners will just accept that they paid the dues for the year, others will ask you to split it, or pay for it all. Totally depends on the transaction. The price can easily shift a few dollars per point depending on the status of the point and the dues. Long, term it makes no difference. Short term, you may either be saving a few hundred bucks if you can't travel for a while to buy one stripped, or saving a few hundred bucks if you can travel before the points expire to buy one loaded.