I don't usually wave first - but return all with a wave or big smile. I haven't found any type of discrimination from any other types of bikes if I do wave first. They've all waved back. My pet peeve is that most threads at some point bash HD. What about it doesn't matter what you ride, but that you ride? (steps off soap box)
Riding a hack, I've gotten quite a few thumbs up from other riders. When my teenage nieces ride with me, they give fist pumps to oncoming riders.