I appreciate the hints/ideas.. Though there's no automatic File History for those user-specific directories and I only manually create System Restoration points for the more significant Windows upgrades/service packs or hardware changes.
It seems that Recuva could restore some of those files that were simply deleted (like the Extensions' directories), but none of the files Opera simply overwrote after resetting all settings.
Apparently I'd have to have a program that actually quarantines those files or at laest logs file changes (like the NILFS file system, or Windows' File History which I never needed before, and also causes System Volume Information to become uncontrollably huge).
There's a "backup" to my Opera files that's a few months old. I honestly won't bother with it though, since it's too old really and too much has changed, so I'm better off with this new profile (except for the synced bookmarks of course).