Interesting question @kenfinkel! Inflation of the daily "rewards pool" increases the number of STEEM tokens held on the blockchain... but it does not directly alter the value of STEEM. (An important distinction.)
From the Steemit FAQ page...
Steem began creates new tokens at a yearly inflation rate of 9.5%. The inflation rate decreases at a rate of 0.5% per year. The inflation will continue decreasing at this pace until the overall inflation rate reaches 0.95%.
So as the ecosystem of Steemit users increase over time, yes, STEEM tokens will be harder to come by. BUT the value of each of those tokens is another story. Ideally, the value rises as the demand rises. There are many other factors that give value to the STEEM ecosystem. If your next question is where does the value come from? This might help...
Steem is a game system where users compete for attention and rewards by bringing content and adding value to the platform. The rewards people earn are tokens that have market value and are readily tradable. It is similar to how someone playing a video game could obtain a limited item or currency by playing the game. If the currency or items are transferable between users, then they can sell or buy them on game item markets.
Very useful.