I think that getting reservations at 7 months is certainly possible at WDW, but depending on when and where you want to stay, getting exactly what you want will be more difficult.
I don't know if I would consider points at VGC to use at WDW, unless I also planned to use them occassionaly at
Disneyland.
We bought BLT because we wanted to be assured we could stay there during our trips and we have the power to book between the 7 - 11 month home resort period. If we stay elsewhere, it will only be by choice. I was able to change to a BCV studio, for the 2 nights I wanted next July, at the 7 month mark.
If you are flexible in where you stay at WDW, then it might be worth it. SSR and OKW, because of their size, tend to be the ones that have more availability at the 7 month mark than other places. But, if you want to get resrvations elsewhere, in, say, December, the 7 month mark might be tough as a lot of
DVC members book at the 11 month mark as this is a very popular DVC time.
Personally, I would buy where I wanted to stay, or at least are okay with staying with most of the time. If the goal is WDW, I would buy one of the WDW resorts.
Good luck!