I never knew that settings were a part of the backup.
Knowing that should make your life so much easier!
The reason I import files as if it is a first time install is I get to see what is really stored in the tags and address it. But I think I could also do a restore then delete the database and import my files accomplishing the same goal.
This is what is creating all the work, and rework, that you have explicitly said on multiple occasions that you do not want to do. Just take Brian's advice and use the Library Backup and Restore process during each major MC upgrade process. This is what I do, unless MC actually finds the previous version Library and uses that automatically, which it often doesn't.
Then if you really want all the tags in your library also in the files, select everything in your library and run "Update tags (from library)". Best not to do the whole Library at once of course, because it would take a long time, and you should check what you are doing on a small group first, then do more in reasonable and definable chunks. That process will write all the MC fields that have been set to be written to file tags (in "Options > Library & Folders > Manage Library Fields > {select a field} > Check "Save in file tags (when possible)", and can be written to the files, to tags in the file or in a Sidecar file.
It can't be easy to find missing tags in files by re-importing and looking at the mess that is created. As timwtheov suggests, use the tools in MC, specifically Views, to check tags if required... after Restoring a backup from the previous version. Learn to use the
Tag() function to directly read a tag from a file, and if you get creative, check that the corresponding Library field has the same value, or only display records where the file tag and the MC field value are different.
For goodness sake, stop re-importing files every year and making work for yourself!