When I had my MG all MG owners waved at one another (when I say all I mean pre-Metro/Maestro/Montego/MGF). I occasionally waved at other classic but rarely got a response. MG's were just too common!
I didn't really have the Stag for very long - so don't remember much about the waves.
With the Landy, all real Landy owners wave at one another - and I'll waved at tricked up or special edition (Camel, G40) Discos, Rangies and Freelanders too.
In the few journeys I've done in the Morgan I've had a biker pull up along side on the M25 and wish me "good morning", I've had waves from a variety of other classic including an early Landy, and I got a wave from a Seven too - so I waved back, dropped a cog and roared away - admittedly we were going in opposite directions.
I like the camaraderie of classic car ownership.