yeah, the no wave thing is pretty bad. I've come to expect it from most C4, C5, C6 guys although I wave regardless but at least almost all C1 thru C3's wave back. Every now and than I come across one that doesn't.
i've stopped getting upset at the other vettes that don't wave back - it's not worth the aggrevation to worry about it, and I figure I at least did my part even if they didn't return the gesture. Besides, there are times that sometimes the other vette just doesn't see you to return the wave because of concentrating on other traffic, fooling with the radio, etc.
I waved at a woman in a C4 once just before turning into a gas station. She looked at me but didn't wave back. Oh well. Next thing I know she pulls into the gas station while I was pumping the gas and asks if we know each other. I realized what hads happened immediately - she wasn't aware of the wave tradition so when I waved she was confused and actually turned around and came back figuring that I must have known her since i had waved. I had to explain the wave tradition to her.
I drive my wife crazy though when we aren't in one of the vettes and we are just driving in one of our daily drivers and I see a vette and I still wave. She thinks i'm nuts because she says that waving is a waste of time since the vette driver has no clue why i'm waving from a Lexus or a 4Runner but it makes me feel better to do it anyway and honestly, it's mostly reflex and habit anyway to wave if I see another vette no matter what I'm driving.