It won't be a popular answer, but the truth is nuke and pave every so often. The problem isn't Arch itself, the problem is that I like to try new things pretty regularly, and occasionally install junk that I don't want long-term, but that I forget to clean up.
Quite a few years back I just started a bash script that stays in my dot files repo, that has all the base packages and configuration in it that I need for a new system. When it's time for a fresh install, I can run that script and have 95% of my system set up. I even include gnome settings and stuff in there using the CLI tools.