Thank you for your support and your comment. There will always be ways to exploit the system, but I think the three items I discussed (expiration of rates, filtering with a blacklist, and requiring of a comment) will reduce both the likelihood and the the impact of a lot of these types of attacks. It would definitely require some flexibility.

I think the User Authority (@steem-ua) uses an algorithm which takes into account some of the things you mention, which is also a great avenue to include. Perhaps the end state would be a compilation of all three scores. There is also a 4th score with @steemchiller's voting CSI score.

One thing to consider is that user feedback offers some qualitative analysis which can't really be represented in the numbers. A person reading the rates left for a specific account can gain a better understanding of that account's presence. Thanks again!