Why keep a rejected meeting in your calendar?
As an expert, I get many invites I just reject outright. But I still want to be available to answer any questions (through a chat, or call-in as needed) that arise in said meeting. So for me, this is a frequent need. Your milage will vary, of course. But to be able to choose "Reject, but keep" would be nice.
And the part about forwarding invites as e-mails (but updates are not effectuated), that's a major issue.
Of course, my major gripe is that when a calendar invite has been sent out, any and every change — even just adding a single item to the agenda — generates a new invite that people must accept or reject. (I prefer to reserve people early and add itemised agendas later.)