Re: First of all, welcome to the Z3 world...more
As I'm sure you already realize, a CAI won't give you that improved exhaust note you're looking for, but if you get a good one, it will give you an improved sound from under the hood. And they're generally not a huge investment, so you're not really risking much.
As far as an aftermarket exhaust, a lot of people have different favorites (typically based on nothing more scientific than what they dropped a few bills on! lol). Personally, I love my Supersprint. Just the perfect tone to my ears.
Congrats on the new ride. But I am a little confused. I have an S52 M Roadster (1999), but I used to have a 2.8, and to me it was plenty peppy. Maybe you need a tune-up? Or maybe you were just expecting too much. I can't say. But no, even my ///M probably couldn't keep up with any number of general commuter type cars out there these days (the one time I took someone up on a little run up the road, I was pretty much left in my tracks by a newish Maxima). We're in that hp wars thing again, and many new cars are quicker than the roadsters we're driving, save for the S54 (2001-02) model ///M's. Hell, there are a number of standard pickups I couldn't win a race against. On the upside, I'm not concerned with 0-60 or quarter mile times. So AFAIC, I still win. :)