If you are really not sure which of those 3 resorts you might like and given the times you are going to be traveling (which are busy for DVC), I might hold off and wait to visit them.
We bought BLT because we knew that is where we wanted to stay and paid extra for the 11 month booking window.
But, VWL is very popular in December and BCV is very popular during Oct. Neither will be easy to get at the 7 month mark for those times.
While I know that BLT has a longer expiration, IMO, but worrying about something that doesn't come in to play for 31 years is not something that should be a major factor in your decision. If BLT is where you are okay staying and won't be disappointed if you couldn't get the others, than getting the extra years is a great benefit.
But, given the price difference, you might be able to secure a few extra points at BCV or VWL to use now, for the next 31 years instead of paying more for less simply to have them down the road.
And, you are correct, depending on when you go, the points difference can be more at BLT than others. We travel in Magic season so for us, BLT, VWL, and BCV are all around the same.
Good luck and take your time. It is a big decision and you should be thrilled with your home resort!