If you pool hop to the OKW pool, you can use the sauna in the lighthouse. I think it's just the ones operated by non-Disney contractors (ie. Niki Bryan - SSR Spa and GF Spa).
that's probably it - the facilities at SSR are not operated by Disney. The contractor may handle that any way they choose, and the contractor at SSR charges.
You could let DVC know that you'd be willing to spend your dues to pay the contractor to allow access to DVC members. But others of us who don't care whether we get to use a sauna or not may not be amenable to an increase in our dues for that reason.
I'm not aware that BCV or BWV actually have steam rooms or saunas...I know OKW has one.
Other resorts aren't running spas that charge customers hefty rates for treatments and use of the facilities. Having used the spa as a customer, I don't think I'd care for it if the facilities were crowded, which I'm sure would happen at least some of the time if members were again allowed free access.