I scanned the first sites of the whitepaper. It is a complex system, but i try to explain it in my words.
Miners get Steem as reward. That is the source of Steem.
Content creators and curators become rewarded in SP and SBD for content creation (amount decided by community through curation) and curators for curating.
SBD can be exchanged into Steem. Why should someone buy SBD? Because you get interests on it. SP can be powered down to Steem over a period of time.
So if the miners mine Steem and then exchange it into SBD, they get even more rewards.
Does I understood it right?
So can the value despite this inflation rise? Are the mining rewards lowered by time?
Steem power can be powered down and this process takes about 12 months to complete and as far as I remember you will be getting your Steem in small proportions over the time being.