Yep, same here. The 335i pops-up on a lot of radars when considering a 350z (at least, it did on mine). It's a different animal though and ultimately, I wanted a tighter, louder, more thrilling experience than a BMW saloon. The other main factors were higher cost (obviously). Would've been looking at nearly double the price of an equivalent mileage 350z (roughly, £8k vs £16k) and all the horror stories I'd heard about reliability. There's probably a reason why a £40k beemer is now selling in the low teens, five years later...
Oh, and as you rightly point out, there are millions of 3-series on the roads. The 350z feels far more exlusive.
I guess it's a very good machine though, with added practicality and fuel economy, if you find a reliable one. Glad to hear you're enjoying it!