Plex feels so incredibly over-monetised that I don't treat it as similar to Kodi or XBMC at all.

Interesting that you feel that way. I suppose compared to free and open source anything seems "incredibly over-monetized", but Plex still seems to be one of the cheaper/simpler business models in software, to me. They've got a generous free tier, a simple subscription service for some nice to haves on top of that, and offer a "lifetime" subscription option if you'd prefer to pay a bunch of months up front and not deal with it again. It seems simple and basic enough to me.

I know they are trying to do some sort of TV channel-like value add subscription as well (because everyone is in the Streaming Wars now), but they don't push upsells into the app itself (or I never have a need to go to the sections that have that, I'm not sure), just random mentions in emails that I mostly ignore.

I contributed a bit to XBMC in the past, and in comparison, .. well, I'm not too sure how to describe this.

Plex is like everything wants to be proxied over the plex.tv cloud, want a plex SSL certificate, tunneling (ok, NAT is common at home and all that) control traffic, $80 one time purchase apps/pass, it feels significantly less like "running a Plex server" and much more like "sign up for a Plex account and link everything to it and link your server to it". Plex Pass also gates a significant amount of features.

It doesn't feel like running your own HTPC/media server anymore, for all intents and purposes it feels like you're paying a Netflix subscription to use your own hard drive, at least to me.