No see I disagree.
Always wave. Wave to anyone on two wheels. Thats bikes, scooters, and motorcycles. Wave to kids in cars, wave to school buses and any emergency vehicle you see.
If someone doesnt wave back its their problem not mine. If they are actually doing it on purpose its very shallow and crappy.
I have a blast on my bike, I want people to know I am having a blast. Think about it, carry the message of we are all brothers and sisters on two wheel. The motor on a bicycle is the most elemental of motors. The scooter rider will bleed the same red blood if he/she goes down that we will. So will the cyclist.
Dont be like the ones that ride for status and as a life style accesory, ride because of the sheer joy. Be the one that waves anyway.
Only my opinions but I believe them to be the better way.
Steve