Oh, I hear you. I have nearly 10TB worth of media on my NAS. I didn't remove old stuff from folders, rather I just stopped using folders going forward. When I made the decision, I just started adding the media file by itself. Sort the folder by Newest from top to bottom. All your older folder movies will scroll to the bottom.
Side note, what is with this filename curating business and dicking around with NFOs? Kodi doesn't ever seem to miss a beat and gets it right every single time.
Well, I'm gonna be honest, I'm waaaaay behind on the curating thing, but it is mainly an anal retentive thing on my part. I prefer everything to be in the same nice neat format when I look at it. As you can see from that screenshot, it is mostly just however it comes down from the torrent creator. Nothing wrong with that really when I am not actively looking at it, and you're right that Kodi and Plex seem to get them 99.9% of the time, so it is mostly an aesthetic thing. However, I also find myself wanting to occasionally replace screeners or HC rips and the like with a better version, and this program I use (tinyMediaManager) makes finding those a snap. Yes, I realize I can just search for dvdscr or HC and find them about as fast. But that program also has a nice rename feature that I love, and I've been wanting to use it to get everything just perfect.
But on top of that, for example, when you have Terminator 2 Director's Cut and also Terminator 2 Skynet Edition, Plex and Kodi don't differentiate the two at all. They just say that you have two versions of Terminator 2 (or they did when I started this process years ago, who the fuck knows, maybe they updated it since). tMM has an option where it will allow me to specify that it is a Director's Cut or something custom, like Skynet Edition, and it will show up in both programs as such, while still treating it as just Terminator 2 for purposes of retrieving artwork and trailers and whatever else I decide I want some day in the future.
So yeah, it is mainly just me wanting shit to look all neat and tidy. No one is ever going to see it but me, and the few people with access to my Plex that might decide to watch both versions of Terminator 2, which is why I've slacked way way behind actually doing it, but it is still something I want to do eventually. Dumb, I know. Don't judge me!