350 here
I think 350 is the perfect number of points if have family of 4 or more, since if you study the charts, the median # of points needed for 1 week stay is 350 points for 2BR villas during "Magic Season" just below the "Premier" season which you can guess implies - Xmas, Thanksgiving - too crowded then anyway. So I bought 350 points resale. I looked specifically for a 350 point contract hoping to find October use year, but ended up with December use year which is fine.
However, we found we need more time at WDW - like 10 days, so am starting to bank & borrow so we can do 10 days WDW, then 5 days DL alternating every other year, but comes out about the same this way so feel no need to "add-on".
Also, I saw a post from DADDIO on Disboards saying he was buying points from the next year allotment for the prime resorts (he currently brokers & rents out points for $13/pnt), by prime I mean the DVC resorts adjacent (easy walk) to Epcot & MK, and he only was interested in minimum of 350 points. All I could guess is his request comes from the fact that most people need the 2BR units for one week, Dream Season, and that means 350 points which appears to be the average. The resorts most requested are: BLT, BCV, & BWV in that order.
I chose to buy at BWV for 3 reasons: the ONLY single level DVC Grand Villas (hard to get - only 5 available so need to own there, plus 2 that are 2 story), easy walk to Epcot & Boardwalk activities, and the RTU that ends in 2042. BLT has RTU that exceeds my life expectancy, and rather have expiration that corresponds with date I expect to stop traveling. BLT may be better purchase for younger people if they prefer MK. I still prefer DL over MK - feels more like real Walt IMO, plus VGC is most amazing of the DVC resorts! If have smaller family (say only 1 child or even no children), then points for 1BR stays or even studios may be better bet (275 points - 1BR, or 150 points - Studio). For those that go every other year, can cut the amount of points needed in half.