I've given up waving to non-helmet wearers, cruiser or sport bike. Not enough return.
The ones that blew me away was during bike week and about 3 different cruisers waving across the median on the highway. I felt bad they surprised me so much I didn't get a wave off.
Edit: I do also try to wave to scooter riders as often as I can, hope it makes up a little for all the flack they might take.