Thanks Nanzo,
What you say about Steem catering for the usefulness of comments works in principle, but not in practice. This is because we have alimited amount of votes per day and comments rarely make more than a few dollars. So somebody who wants to make money with their votes will not curate comments, add to that, the fact that down voting appears to negatively effect your influence and we have a run away, non-curation effect.
I agree with what you're saying about the how the post is being shared and a good share will be well curated and be shared to a decent sized audience.
However, even a bot sharing will have value for Steemit as it will positively effect Steemit ranking values, also sharing on its own has more value than voting, but voting, sharing and commenting on the original will have loads more value. Bots will find it hard for this to do, if they can do it well, they will be indistinguishable from human contributors; which will be good I think.
make it sense to you that you combine with your idea this one...
https://steemit.com/steemit-ideas/@liondani/separate-voting-power-for-post-and-responses