I've done cross-grades on old ARM devices, as Debian gained repos built with more optimizations, and I've done in-place 'upgrades' between different Debian-base

I've done cross-grades on old ARM devices, as Debian gained repos built with more optimizations, and I've done in-place 'upgrades' between different Debian-based distros (e.g., Mint Debian -> Kubuntu). As long as you have a busybox with a working dpkg in it, it's pretty easy to deal with any dpkg or apt errors you encounter as you see them. If you use these same strategies between Ubuntu releases, you can also 'push through' any brokenness or quirks that the normal wrappers for this process bail and reverse on. If you run any Debian-based distro, just doing one or two upgrades like this will really liberate you from worrying much about your package manager getting 'broken', and spare you from ever doing clean reinstalld unless you really want to.