It is not impossible to change out at 7 months and many members have had great luck. However, it does depend on when you go and what you want. Certain things are going to be extremely difficult unless you own there (AKV Concierge, BLT MK or Standard View, VWL in December or the Epcot resorts during F & W).
I personally would not buy VB with the intent on only using it at WDW. The pricer per point is cheaper, but the MF's are not and any savings you have upfront will be eaten away with those higher fees.
If you think staying at SSR while in WDW is okay, then I would buy there. The MF's are lower than VB, the contract expires in 2054 (vs. 2042 at VB), and the price per point is only $10.00 - $15.00 more, not enough, IMHO, to buy at VB. SSR is really a great deal for those that want to vacation in WDW.
And, if you own at SSR, you know that you can make reservations at WDW 11 months out. With VB, you can't book at WDW until 7 months. If what you want is not available, you will be stuck. You could end up having to change resorts several times to piece together a trip.
I bought at BLT because I only want to stay there. Price per point was obviously more, but where I stay is important and I want to be able to book it at 11 months--didn't want to leave anything to chance.
Good luck!