I must confess that I have never worried about "friending" and "unfriending" people on social media. Maybe because I rarely use the resident tools to track people I keep up with.
Mostly my interactions are sorted into bookmark folders of my own creation, which allow me to keep track of my "core group" and "2nd tier" and I also have one that's "Interesting but inactive" that I occasionally check in on... and then there's "everybody else" whom (I confess) I rarely get to.
One of the things Facebook and twitter DO have that I find lacking on Steemit is the ability to sort people I follow into "groups." I follow some 500+ people, and it's a LOT of work to keep up with them using the Steemit interface... which is basically just "a long list," as you know.
Would I unfollow someone? Maybe for similar reasons as you describe... if someone who "used to be interesting" became a sellout slave to bid bots. Or if they started posting plagiarized or abusive content.
Keeping track of 500 must be hard and you must miss things sometimes. You cant please everyone can you?