DVC should never be purchased for future resale value.
In general, DVC keeps the value high due to its use of ROFR (right of first refusal) to buy contracts with too low of a price.
It is true that overall, DVC has retained value better than the general timeshare market...but that can always change.
I believe during the 2008 crash, there were some DVC contracts bought in the $70-90/point selling in the $30/point range...and DVC didn't seem to ROFR many contracts during that time of declining values.
You can look at the ROFR thread
http://www.disboards.com/threads/ro...ost-for-instructions-formatting-tool.3551378/
to see how resales seem to be trending for other monorail resorts ... but no other resort is all studio like Poly, so it's not an exact science.