I'll wave at pretty much anything on 2 wheels. Most of the time I don't even know it's a scooter until we pass, then I realize that it was. The scooter rider is usually in amazement that I waved.
Most of the metric cruisers will wave back at me, and very few of the Harley types will wave. I'm talking the hardcore, wallnut shell (if their wearing a helmet) leather chap, bike barely running, I'm cooler than you types. It's nice when I see a big group of Harleys riding, cause most of them respect your ride and will wave.
Yesterday riding through a neighborhood I saw a little kid on one of those looks like a chopper bicycles. He waved at me so I waved back. looked like it made his day.