I dont always see a wrx/sti until it's too late or I'm shifting/turning/driving etc. I wave when I can, sometimes I get a response, sometimes I miss responding.
Got a wave from a guy in his 50s in his 72 charger (Petty blue I think?) with a bumper sticker that read "Yes, it's fast. No, you can't drive it" He was ambling along just like I was. No need to measure penises. The three 370z's I saw all made a production out of passing me that day. I get a lot of that from the 370/g35 crowd. It is amusing, but I'm not a racer so I lose a lot of races I am not even aware I am running.