I don't know if I would buy HH or VB with the sole intention of using them at WDW.
There could be benefits to buying at one of the less expensive WDW resorts resale over BLT to save money if you are okay with possibly not getting BLT for the times that you want.
SSR and OKW offer some good value as well but would give you an 11 month booking advantage onsite, something HH would not do. At least with one of these, you could book something for your travel and then at 7 months, try and change. If BLT wasn't available, then at least you would have something to fall back on.
But, I think it really comes down to how important is staying at BLT to your plans. If you really want to be there and will be disappointed if you can't get it, then I would buy there, money aside.
We went through this last year and in the end, went with BLT, for about $5000 more than buying SSR resale. Why? Because we knew we had no desire to stay at SSR. We wanted BLT because the CR has always been our favorite location. MK is our favorite park and we said we would only buy
DVC when walking to/from that park was an option.
Of course, they built BLT so we bought. We figured that over the course of membership, that $5000 really doesn't amount to that much in order to ensure we are at the resort we know we love. If we want to trade out (and we have), we can, but at least if it doesn't pan out, we are still happy.
Some love to resort hop and are really fine with staying at all the DVC resorts. If this is you, then definitely consider buying at one of thoe less expensive resorts.
However, since the membership is increasing and there are more DVC resorts now, availability at 7 months will become more difficult, IMO.
Good luck!