I think it will depend on the popularity/numbers on the road. When just 08 SRT's are on the road, I think the wave would probably be popular, because it would be uncommon to see another. If the 09's start flooding the road with challengers, "wave fatigue" might set in. I do not have the forumula for what a critical mass would be, but it might be fun to work out how many sightings per day a person has before they get tired of waving.

I think it also is correlated to how closely a vehicle is associated with a certain personality or type of person, i.e. "It's a Jeep thing".