A.M.
It drives me crazy that people don't RSVP, I think it one of the rudest things that you can do to someone. That said, I would make phone calls and just follow up without making them feel bad. Honestly, some people were just never taught how to act properly and they don't know any better.
If you want to send a follow up note instead of calling, I think that is ok too but I would make it something like a Last Call type funny email. However, I would not include those that did already RSVP. They already did the right thing and RSVP'd so no need to send them another email/correspondence that they have to read and deal with.
Good luck!