I think having a page with the list of the last actions made with ability to undo them would be super helpful, especially for the bulk operations
Operations may not be undoable after a bit of time (like undeleting files after clicking Empty Trash). Would it still be useful to try to undo what can still be undone?
Obviously if the action can’t be undone, the undo button has to be disabled 
But if it could be partially undone… my first instinct is to at least do what you can (I.e. recover at least some of them), but there are probably some edge scenarios where that will make a bigger mess.
I still lean towards do what you can back toward ‘correctness’.