Back in the day MG drivers almost always waved but there was a hierarchy to it. Midget drivers to fellow midget owners and B owners to B owners. I thought this was very poor so when I got my MGB I waved at them all.
Driving back into Newton Abbot yesterday afternoon there was the usual holdup on the dual carriageway and an E89 came up behind me. We both had our roofs down, I waited for a wave or a light flash, nothing, so after my success with the Z3 owner the day before I gave a massage wave. Nothing, miserable gits.
In the E86 I've only ever had waves or flashes returned by Z's but the odd MX5 owner has mistakenly waved at me. When I drove the E85 with the roof down I got waves and flashes from just about anything else with the roof down, happy days
I will always wave at other Z4 drivers. The same as I have always waved at other MK1 TT drivers. Problem is I have never seen another Z4 driver on the road yet, so I wait in anticipation for the wave back!