Tom
Beta Return
One concern I would have with buying VB or HHI with the intent on using those points to mostly stay at WDW is there is always the possibility that VB/HHI could be sold off or somehow separated from the WDW pool and you would have points that could not be used at WDW.
I don't know all the legalities, so don't quote me on this, but since the points are technically DVC points, I don't think an owner at HHI or VB would be harnessed to the new Owners of those resorts. Disney would simply buy back the contracts as part of the sale, and probably allow (encourage) you to buy into DVC elsewhere.
Regardless, I would never buy points at HHI or VB, simply for the fact that I never plan to visit those resorts, and because I want my fall-back resort to be on property (SSR), if nothing else is available.
Also, 600 points is WAY too big for one contract. That's for someone who's retired and wants to live at HHI or VB for half the year. Definitely not for a casual WDW visitor.