Been using an install from 2012. Cloned every time I moved laptops or internal storage drives. Two surviving clones, one main laptop and older laptop as home server and backup.
Haven't had to do much, really. Just regular package updates (including AUR ones) and cleanup of stale packages. The main laptop gets updates applied frequently, but the backup only once every six months / a year, except security updates (e.g., ssh, OpenSSL, the recent xz backdoor was a no-op because I hadn't ever updated the backup to a vulnerable version). Then there was the KDE 6 release recently.
Every once in a while I go through the list of every package installed and see if I should remove any. This is a no-op for most packages, since they are usually mandatory dependencies of another package, but there's always some packages I'd installed for some limited purpose that no longer applies.
I've cleaned up dead config files a few times. Especially around KDE major version updates. Not that it took up too much space or broke anything; just that I didn't want those files around.
I've kept around a bootable USB key for emergencies, but now that I think about it, I'm surprised I've never had to use it for a system rescue. There was that one time I changed my password and promptly forgot the new one. But it's been such a long time since I've used it.