Yes there is a lot if crap on steemit, but those people will get bored when they don't earn the money they want and either leave or improve their quality. I do think comment rewards should be better, I comment a lot (like this) and I try to add value but people do forget to up votes comments a lot. I think curating should be looked at on one hand you need huge steem power to earn anything from curating and you need to be in the first 5, but clearly we don't want to make an upvote platform and there are already a lot of bots up voting rubbish.

In terms of replacing Bitcoin or Etherium with STEEM I think the whole notion of one crypto is not only a really bad idea from a cryptocurrency resiliency perspective but is not even needed. I see a time with AI multiwallets that will look at your holding and your transaction an decide which currency is best to use. Building an economy is hard, but as the network effect grows the economy will evolve on its own, this just needs time.