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I know but you can't be sure that increase in price compensates for the decrease in rewards. I get what you are saying but we can't be sure of anything, we can only speculate.

the more users there are, the more incentive there is for people/groups to want to buy steem power to influence the traffic on the site - so gradually it will become much more attractive to buy into steem just for marketing purposes.
i'm not sure the payout levels will go up or down - but there will be increasing amounts of options for increasing your payout due to new services (e.g. utopian). more users = more potential.