I usually will do the "two finger down" wave to just about anyone that have their face in the wind. I don't bother much in town of course, but out on the open rode, it's all good.
Ugly John
If I'm where I can wave safely I will. If my wife is on the back she does. I don't pay much attention as to whether the other rider waves back, except in town. Most of the little guys on bicycles actually stop and wave. Some have even tried to race me down the street. I admit, a few have even won.
That reminds me of a joke I must post.