Nobody knows how much SMT's will increase the value of Steem. But it's a bit like this... Remember when Macs were considered better than Windows except for the fact that nobody was writing apps for that platform? The more developers of their own websites use SMT's to interact with the Steem blockchain, the more the Steem blockchain will be worth.
I could set up my "zoidcoin" on astrology-x-files.com and have those little green upvote buttons (or something similar) that would replace popup AD's. (I don't have AD's on my site anyway, but many do).
In the future, most businesses will have their own currency and will need a way to swap currencies given an exchange rate. SMT's are smart contracts that work between your website and the Steem blockchain. So if you're confused about SMT's, then maybe you should study smart contracts and the architecture of Ethereum.
Personally I have my doubts that Ethereum can scale. Scharding looks more like a bandaid on a broken model than a real fix to me. They have the network effect right now, but once Dan Larimer complete's EOS in June, it will be as fast or faster than Bitshares and Steem. EOS is a generalization of the ideas behind Steem for social media, but will be used for all sorts of logistical problems such as relaying medical information by elimination of informational siloes while keeping confidentiality, etc...
The other reason why I think EOS could replace Ethereum is that solidity was a special language that Vitalik wrote for the Ethereum blockchain which is difficult to work with. EOS developers will be able to use C, C++ directly.