Would it be possible some automatic search on each post to show how strongly it is copywise related to other posts? It would be a robot version of what you say you do "When I come across a longer post, I often will google search some of the content to see if it was copy and pasted from anywhere else, word for word."
It could even give a % how much is a copy paste of previous contents and of course provide the link to that content. I am not a dev but I can imagine with todays AI tech it should be possible to do something like this.