This could be good idea actually, I like the reputation system of steamtrades. But the rep in there is basing on only one thing it won't fit with steemit system.
Your idea of voting like a witness is better, I think it can be easily abused (make +1000 accounts and make them +rep people you like and -rep people you don't like.) But it's still a good proposal.
Witness votes are stake-weighted, and 'Good Quality Content Creator' would also be stake weighted.
Create 1000 accounts and you have gained no extra reputation.
Did you check how witness votes work in Steem right now?
No I didn't ... I thought everyone had the same input. Maybe I should research it sometime.