I cant help you, but i am searching for exactly the same function!
It is not always a problem for admin account. We have some courses wich make calendar entries every day and all teachers are members of these courses but the fewest need these entries!
So i am looking for a possibility to choose, which course entries are important for me and which not.
Even more when i export the calendar!
Maybe the calendar plugin needs a feature where you can have more eventtypes than "global, user, course, site" or some sort of sub-categories.
In google calendar you can choose which event is for which calendar(eventtype) and turn it on or off. And you can make your own calendar(eventtypes). I think this should be as good for the moodle calendar.