I think one egg casserole should be fine for the size (or the ones who at least RSVP'd). For me, eggs are really filling, so unless its a freakishly amazing casserole that everyone wants a bite of, it should be enough.
I remember we had a great fruit platter at my step-mom's babyshower and they had two or three dips that went with it. I can't remember what was all in them for the life of me, but you could look up some good ones online. With the amount of food you have and drinks it sounds like plenty. If people show up who didn't RSVP and don't get a plate of food, well, their loss