I would separate the good from the deliberately bad (who just do not belong). At the same time, I would also sub-categorise, so there would be more than three facets for us to consider.
The rest (good of various degrees), I think of us as a molecule which makes up all STEEMIT/STEEM are made of. Remove one atom from the molecule and it no longer can hold together as the molecule it was and becomes a totally different kind of molecule.
If we like what we have, then it is not just matter of getting rid of the bad, I agree with you that we need to devise methods to reward those who contribute the most (each within their own sphere of interest, we cannot judge an author against a witness, for instance). The problem is, how do we make such a judgement? For instance, do we solely count number of posts and comments or by the number of people who enjoyed their post and said so? It cannot be according to some kind of mechanistic formula, liking 'trending' for all mechanistic systems are open to manipulation.
As for me, I prefer to let others work on this, for I do not have an analytical mind, so I might as well concentrate on my imagination and what it creates, while also keeping an eye open for the possibilities of making new friends.