I should add that we aren't considering OKW or SSR at all. Too far from the parks,
I'm always amused by these comments -- especially from folks considering AKV!

SSR and OKW to MK is quicker than AKV to AK!
We always drive and can be anywhere onsite in 15 minutes, but if you bus, the buses at OKW are usually rated the best at WDW. SSR buses can be problematic for a couple of reasons...especially if you are staying at THV. Both resorts offer a very enjoyable boatride to DTD, which is also walkable from both resorts.
BLT is obviously convenient to MK, and less so to Epcot -- but not at all for AK or DHS or DTD.
AKV is as far from everything at WDW as you can be and still be onsite. Many
offsite hotels and resorts are closer to MK than AKV.
aren't attracted to the theme...
We like the theme at OKW; SSR not so much. To us, the advantages of OKW are the MUCH larger villas, lower points costs (40% fewer points per night than most
DVC resorts) and relaxed atmosphere. With SSR, THV is a big plus, although the bus situation there is poor.
We haven't stayed at BLT, but from
lots of owner comments here on the DIS, the basic theme there seems to be "cheap construction, falling apart quickly!"
Well...that's in the eye of the beholder. Take a look at all the never-ending timeshares for sale for $1 with free closing on eBay. They are offerred for sale by owners trying to get
out from under their annual maintenance fees. 30 years from now, you may feel the same about DVC.
Directly to your point, with SSR or OKW extended, the difference is only 3 years, I believe -- 2057 vs 2060. I don't see that as a difference worth worrying about.
If you're paying $65 per point for 2042 OKW resale vs. $130 for BLT direct, half-price more than makes up for 18 years difference in term of ownership IMHO. And, if it's
that important, you can buy OKW for $65 (or less) and pay the $25 pp to extend to 2057 and still be WAY ahead.
Bottom line: My advice is NOT to purchase any resort where you would be
disappointed to stay.
And I would carefully examine each little "conventional wisdom tip" very carefully to make sure 1) it actually makes sense when you think it through, and 2) it has some relevance to your family. A lot of "conventional wisdom" concerns trivial aspects of DVC ownership which may have no relevance at all for your family.