Very interesting, but please use tripod :)
I think that:

1. Increasing the user base is good. More people mean more real economy and real market forces.
2. Distributing the reward pool among more users will be not a problem in long run. As market forces increase the price of the steem will go up and getting 1 steem in the future (with price 10USD) will be better then getting 3 steem now (with current price 0.9 USD).
3. What steemit lacks is real middle class (many and many dolphins) if there are 10 000 active users with SP over 5000 any SCAM or SPAM will be detected and punished in matter of hours. Bots are part of the solution. Yes bots are used to vote for anything but in long run quality will grow and will become the middle class of Steemit. And if you get so many people that care about quality content the price of STEEM will grow.