I could be wrong, but I get the feeling this will be the OP's daily drive. On motorway runs it is by no means quiet. Assuming you have a decent seal on the soft top or hard top, and thus no wind noise, you do get quite a bit of tyre noise, and then there's then engine. As above, car does circa 4k rpm at 70 in 6th, so engine noise is a factor. You shouldn't have to shout to speak to someone in the passenger seat, but its far from silent, and I imagine, a far cry from the cabin of a TT if my gf's Golf is anything to go by.
But then most people wouldnt buy an S2000 to chew up motorway miles......
On the insurance note of the hard top, we all know it's a sad fact soft tops do attract vandals and, I assume, occasionally get damaged. I use my hard top in winter, which I suppose reduces that risk for at least 4 months a year. Yes its removable, yes its stupid the way insurance works and yes Im stating the obvious, but maybe one can assume the majority of people with hard tops use them, and thus insurance claims on "GT's" is fewer. But a word of warning, when I bought my car, I had this same issue; cheaper to insure a GT. When I asked Elephant I think it was, if buying a Roadster and adding a hardtop would constitute a GT, they said no, and that it would be declared as some kind of "mod" and actually incur an insurance hike..... go figure.
I might have missed another point, but is the OP considering a TT coupe or roadtser? As I think you need to make a decision as to whether you want to pose around topless.