Don't worry folks you're not mental! I always have waved at people driving the same car as me as I've almost always had less common ones, which I would count as cars you might only see 2-3 of in one day. Whenever I drove the old Merc I sold a couple of weeks ago I got about a 20% response to waves/flashes from people driving the same model. I don't bother when driving my newer Merc as there so many of them around.
So my theory is true marque/car lovers will always wave back (if they see you that is) because they understand why we are waving, whereas people who just happen to have the car probably think we are nutters. (I also will wave/flash or give the thumbs up to any other nice classic car and they usually will wave back - which I reckon helps to prove my theory)
We also have a 1975 VW Camper and 99.99% of VW campers always wave/flash to each other - plus loads of other random people.
So back to the Alfa Wave - my score since picking up my 159 last saturday..............a big fat zero from all Alfas so far. I drive past about 5 or 6 (mostly 156s or 147s) each way going to and from work. I see some of them every day, so my cunning plan is to wave/flash every time until they get the idea. I'll let you know how I get on.
Keep on waving dudes!
