SMTs are really a protocol enabling the constructing of other tokens built upon the steem blockchain. Through there, there will be other new cryptos created for specific purposes. All these cryptos will be on the steem blockchain which will increase the value of that platform. Hence, we should see the demand for steem increase since many of the tokens will derive their value (at least initially) from steem.

As for the second part, you are correct. There will be thousands of blockchains, some public, many private...all dealing with different aspects of life. However, many of the private ones will have to be tied into the public, much akin to the internet now. Private intranets access the world wide web.

Of course, this is all conjecture since the blockchain world is still rather young....we will see how things are built out.