I'm not sure if the restriction on how many e-mails can go out for one event is intended to reduce the load on the system, or simply to reduce clutter in people's inboxes. I imagine there is plenty of bandwidth on campus to send out tons of e-mails. What we're running out of is patience. Waking up and seeing 15 new e-mails, 14 of which you couldn't care less about is just plain obnoxious, and I can't really fault people for simply deleting them all without reading carefully.
Still, I think the suggestion of combining the overnight e-mails into one "newsletter" style message with a table of contents is a good idea. I don't imagine it would affect bandwidth much, but it would reduce clutter a great deal.
For that matter, perhaps the nightly e-mails should go away all together, and be replaced with a weekly or every other day sort of activities newsletter, kind of like the "things to do this weekend" e-mail that goes out every week. It would be more effective probably becauase it would be much easier to look up dates and times in a single e-mail, as opposed to trying to find that one e-mail you seem to recall getting a few days ago about something that sounded vaguely interesting going on in the Space tonight.