Virtual libraries are quite nifty, yes. Just use a tag for each and have the virtual libraries match the tags.
You can even make the virtual libraries appear as different tabs in the main library.
If Library Maintenance isn't showing up, I will hazard a guess that you have a connected device.

That will hide the option.
If that isn't the problem then

but you can always resort to the CLI:
Code:
calibredb restore_database --really-do-it