I'm assuming Ashley was mainly answering what i proposed (warning and allowing to copy with a new name).
Personally I would still like to see a list of problems found (similar to the list find in project), and be allowed to paste duplicate objects with an extra _copy, _new, ...
As i see it i would paste the events on a clean sheet (duplicating anything needed with the extra _) and then go 1 by 1 switching the "reference_copy" to "reference", and delete the extra stuff. (would be more useful the bigger the number of things to change between projects)
But what about the suggestion of copying also missing objects if no "collisions" are verified when comparing the missing names of objects connected to the events that are being copied? (ex. objects just don't exist in the new projet)