I'm going to add one more thing - As @smooth has said to me on many occasions we need to incentivize downvoting for those who have the reputation and SP to do it and also do it responsibly. I would also include in that incentivizing helping new users to the platform that are misguided without creating a spam bot.
When I started with @steemcleaners we gave incentives with upvotes to do just this in addition to SP rewards. Since our delegation we can no longer upvote.
I don't think effective solutions here would be 100% automated.