According to the Steem white paper, the value of the blockchain is intended to be in the attention (= approximated by the web traffic generated) attracted by the content. That attention is valuable to promoters and advertisers who have an incentive to purchase Steem Power help attract even more attention to their content on the Steem blockchain. The current web traffic generated by steemit.com (the other UI's are insignificant at least for now) is nowhere as much as to justify the current price of STEEM (or SBD). The value of STEEM is laden with future expectations of growth as is common in case of growth stocks on the stock market. Time will tell if that valuation is justified. You should note that even the current value of STEEM of 1.8 or so is very speculative. Nothing wrong with that, though, because Steem is very scalable and has a number of exciting nascent applications.