Maybe we could think and suggest better if we first ask Mark...
How much do you need per group?
How much do you need per member...
To fund all that must be funded, including 'growth.'
Pointing out that at 5$/groups we join would cause me to drop all but 1 or 3 groups I'm in (of perhaps 30, most of which I am inactive in,) is a cumbersome way to describe our potential to pay... aside from the difficulty of payment if it is done group by group. Rewarding non-posters who lower bandwidth is a recipie for failing lists. Maybe rewarding those who don't read online helps, but then Premium is shot in the foot.