I got my 09 WRX about 6 months ago. At the time I hadn't seen any others on the road.
I'm a courier so I serve my 8 hours a day in traffic, and I watch traffic like a pedophile at DisneyLand. Predatory on anything that might entertain me, or serve as my rabbit. In other words, I am exceptionally observant. But I never noticed the WRX's waving at each other.
I didn't get a new WRX to deliver things in. It's an indulgence reserved for twisty back roads, and I prefer to enjoy my car and all its grippy goodness all by myself in the pre-dawn hours. In a time and place that nobody cares to be in, but me.
Exploring, building a new route, is best done when the sun is up. Mentally cataloging for future reference. I've noticed that while I was doing this I would run across other WRX's and everytime I saw them they would wave at me. But no other driver did.
I've experienced that on narrow roads. People will slow and scoot over, and wave as they pass each other. But these weren't narrow places. Obscure, but not narrow. (Treasures for people like me).
I became under the impression that WRX people just wave at each other, and maybe I just never noticed. So when I got back to civilization I tried it. He looked back at me confused. I tried it a few more times and got the same result, plus a woman passenger that slapped the male driver I waved at. That was kinda funny!
So what's the deal? Is it a WRX thing? Is it an "I know what you're doing out here" thing? Is it just regional?
What's up with that wave?