We have very few newbies coming in, and I doubt changing the signup in that way will reduce the numbers. In fact, I suspect it might have the opposite effect. Also, spam is a massive pain in the ass.
Just three regularly engaged users can have a significant impact on this place. Signaling from the outset that Hubski is clearly more interested in users than growth might be beneficial.
I can definitely tweak the rate at which a hubwheel is earned.