Nice repo. Did you look at rana? Or other client PoW code? Or just start fresh? While computing power spans a wide range, as you say, even a little bit of PoW makes creating a new account ONE MILLION times harder. That takes less than a second though. There is no ideal amount of PoW that keeps out spammers, but if you can slow them down one-million fold with a trick that costs very little, it still seems worth it.