Re:
In summer I ride steel, in winter I ride "cheap carbon" (which was not cheap at all), I wear whatever kit is appropriate, team, matchy matchy, warm when needed, dry when it is wet, and I long ago discovered that my kits is neither bright enough, nor dark enough for me to consider myself a 'serious cyclists', I have also observed on many occasions the 'cloud of gloom' that sits over serious cyclists.
All of that said, I went to a 6 hour mtb race on Saturday that my daughter was taking part in, as she passed us on her second stint we got no reaction from her at all as my wife, her partner and I jumped about making suitable silly and encouraging noises, it turns out that was the fastest lap by a female rider in the race and that she was on the winning female team, so maybe these grumpy riders who do not acknowledge the presence of a fellow enthusiasts are just leaving it all on the road, or maybe they just don't identify with the whole cycling fraternity.
From a personal point of view, I give a small but observable wave to all cyclists coming the other way and a hello or a thumbs up to all those I pass, sometimes I get a wave or a hello back, sometimes I don't. I also say hello to all cyclist I see when I'm riding my horse, as I think there is at times a perceived barrier between fellow vulnerable road users, erected by both arrogant cyclist and poor jockeys who blame cyclist (or car drivers, or sheep, or crisps packets, or gates) for their own lack of horse riding skill.