I'm running LMS on a Mac where among many other things LMS stores installed plugins in my user's cache folder.

The problem is: it's not a very safe place to store stuff in because every now and then the entire cache folder gets deleted due to (major) OS updates, trouble shooting and what not.
Ideally, I could just do another LMS rescan and be done with it. BUT the installed plugins got deleted (as part of the cache folder) and I need to reinstall all of the plugins. Plus at some point, some plugins that are no longer available in any repo may be gone for good.
Especially, since the Cache folder is excluded from most backups by design/default, TimeMachine is just one example. So I wouldn't be able to recover lost plugins if they couldn't be re-downloaded from their repos.

I know this seems like a small matter and I don't know how this is handled on other OS.

Talking for the Mac version: couldn't you move just this "installed plugins" folder somewhere safe to ensure minimal downtime/hassle when the cache folder gets deleted again?
Maybe to the Applications Support folder (~/Library/Application Support/)? I think that one already has a Squeezebox subfolder in it where you could put it.

Oh, BTW, I get a codesigning related warning ("not a verified developer...") since the last 2 Mac OSX installer packages (beta).

Thank you.