I ride in team kit (Microsoft) as they are our club's sponsor aswell, I have expensive bikes and I'm sure many people out there think I am a snob. I am also an utter goofball when I am out on my bikes, and usually wave, say hello to other riders, runners, people walking their dogs or riding their horses. I also often take alot of newbies out on training rides and help them to get used to bunch riding skills, drafting and conserving energy on climbs etc.
I usually also ride to and from our club rides which as an additional 40km that I do solo, and usually I use this time to ride tempo, or to do a few intervals etc, so I sometimes "zone". Notwithstanding the effort, I will still acknowledge other people out there exercising, if I see them. The only time I won't is if I need to focus on holes in the road, cars at intersections etc.
Oh, and I have blown off a few roadie bunches on my MTB when I have been riding to an offroad ride. That is the only time I would consider myself a snob.
I don't really care whether people greet me, or return the acknowledgement.