[jalcaid001]

I see I have old .db files (from previous versions)
Other files I don't recognize: DEATHScache.db  DEATHScache.db-shm DEATHScache.db-wal, onechannelcache.db

Do any of them serve any purpose, or I can delete them?

[Karellen]

I see I have old .db files (from previous versions)

Here are the database versions per Kodi release... https://kodi.wiki/view/Databases#Database_Versions
It is safe to delete the older ones.

As for the other databases, never heard of them, but I'll take a stab and say they are from (banned) addons