The more people that power up in the long run = higher STEEM price. The more incentive we create to power up = higher STEEM price. Simple.
STEEM is more of a company share that is liquid - holding STEEM is an investment in this platform. Holding STEEM POWER is a form of locking your shares up and earning extra interest on them, separate from the interest you would be getting holding STEEM. Steem value has potential to grow still so thats where the interest would come from. The higher steem value = higher payouts for SP holders and is also good for STEEM holders. Its a win win for both.
Steem Dollars are a good stable place for your money. People forget its not only pegged to the USD its pegged to $1 USD worth of STEEM. People seem to misunderstand this and say " Steem Dollar is $1 USD" when in reality it is $1 USD worth of STEEM and always will be. So for example I hold STEEM as an investment, keep some locked up in SP so I can earn more interest. As the price of STEEM rises I will put more of my STEEM holdings into SP as well as the money I need to spend for the year into STEEM DOLLARS. STEEM will remain as a share or investment token and my SP is another account for those shares that earns me more interest. The price of STEEM will probably find an equilibrium price and it will be much higher than where it is today.
HOW MUCH STEEM IS AVAILABLE TO BUY?
For people who are new to trading in the alt coin space I want to clear up Steems coin supply. The economics of Steem can be hard to decipher so I hope this helps you guys. From what I understand based on the following math this is the amount of liquid steem available on all exchanges.
if you look along the right hand side of steemd.com
current_supply and total_vesting_fund_steem are the relevant ones
current_supply - total_vesting_fund_steem = liquid steem
1 - (total_vesting_fund_steem / current supply) = ~97.1%
115,797,075.616 STEEM - total_vesting_fund_steem
112,480,690.235 STEEM
= 3,316,385.381 LIQUID STEEM avail across all exchanges as of writing this article
There is less STEEM in circulation than Bitcoin or Ether at the moment. Keep this in mind. See 
https://steemit.com/steem/@dan/supply-of-steem-decreasing