I don't think the scene is dying at all, just growing up.
You don't see the huge wings, the altezza lights, the fartcans, and stickers anymore because people are growing up and realizing that part is rediculous. I know many people whom I work with that are still heavily into the import scene. Their forums are still thick with members and the aftermarket is still huge. It's that they are finally focusing on performance modifications and steering away from the BS parts. Many of these imports you are seeing are probalby sleepers. I got taken by a MkV GTI a while ago. I looked stock but got me by about 2 cars after we hit 70. I did some research on them and they have all types of pop and swap ECU's that give between 50-70hp with only and intake and exhaust and on pump gas. If you swap for a bigger turbo you can see 100+ gains. This guy must have been running low 13's in a FWD Volkswagen!
My point is it's still alive, just all grown up.