Becoming a family of 6 is exactly what tipped it to being a good value for us. Before that, we could always stay in any hotel room anywhere, on little notice, and for about the same price. But once you're 6, that no longer works. Enter
DVC... you can get 2B's which sleep 6 comfortably or 9 if you cram. We fit nicely, adults in the master suite and kids in the 2nd bedroom. As they get older maybe 1 or 2 of them will move out to the sleepers. If you're looking to be near the Poly then buy at BLT. Yes, your concern about being far from the action at the AK is pretty important. Driving is fine, but I wouldn't want to commit to a lifetime of driving while at Disney. I will happily stay there on occasion, but long-term if I'm going to own somewhere I want to own near the Magic Kingdom.
How many nights do you stay? I'd buy around 160. That'll get you 320 every 2 years, which is enough for a 6-7 night stay in the 2B. Should run you around $18,000.