Is there a way to separate audit activities from "real" actvitites in a case?
I had one site where they asked me to have it automatically put the "copy sent to" activities into the trash, so they're still there but don't show unless you use the filter accordion to see them. It's not efficient database-wise, but for low volume is a possibility. At the time extensions didn't exist yet, or maybe were just starting, so it was implemented by overriding a core file. You might be able to do something similar with hook_civicrm_post, and while not robust, the subject lines are mostly identifiable so could filter based on that and set is_deleted=1.