I see Kewl's point regarding the value of the 3-series and agree.

With that being said, I generally don't wave to any 3-series, unless they have some special unique features (M's, special packages/mods that show they are into their cars). Most 3-series drivers (and 5-series and X5 drivers, for that matter) aren't necessarily fans of the car or marque. They simply drive it, often not knowing much if anything about the car they drive. It doesn't matter what's under the skin for most of them, as long as there are roundel badges on the surface.

In the early days I've waved to X5's while in my X5 and gotten blank stares or no response. The only time I get flashed or waved to/back at is when I'm in my Z3, mostly by Z3 and Z4 drivers.