I actually really like your mock-up and really appreciate that you took the time to make it. Hopefully you don't mind if I take quite a bit of inspiration from it, because I definitely think it looks much better than my current one.
Yeah, I agree that the network effect is one of the biggest problems. Retention seems very tricky with a concept like this because while posting it to reddit or HN can result in many registrations, few people stick around because there isn't much to do on the site because there's so few users at the moment. It honestly does make motivation pretty difficult, but I am indeed going to stick with it regardless.
With regard to your last 4 numbered points, currently 0% == not answered == neutral, and this is mostly due to technical limitations. Your default similarity cube is just (0.0, 0.0, 0.0, 0.0, 0.0, ..., 0.0) (50 zeroes), and voting on cards adjusts this accordingly. Such that if you answer 100% to every card in the first cluster and answer no other cards then your CUBE would look like (1.0, 0.0, 0.0, 0.0, 0.0, ..., 0.0)
I was thinking about a potential way to solve this, but as of right now due to the constraints of CUBE similarity matching, this is the current solution.
Thanks again for such an insightful reply!