I wanted to suggest to get the underside of your car covered up, but then saw you already mentioned that.
Since you're going for performance mods, that definately would be a good step.
If not all of the underbody, then at least do the front since you already have the Type R hood.
I promise you that you will notice the difference at high speeds.
And don't forget the under the hood air deflector.
A set of good and bigger air deflector to cool your brakes.
Seat you also already mentioned. I've been using the Recaro PP seats and absolutely love them now I have gotten used to them but I remember you posted once that you are a bit too big to fit it them.
What about a smaller and lighter steering wheel (I'm contemplating that right now).
Type-R carpet would look nice in your car too I think.
Second, there are lots and lots of small bolts and nuts everywhere in your car just holding things in place which otherwise have no structural benefit.
Perhaps replacing these with aluminum of titanium ones would save more weight than you might think.
Also, I have one of those broad-view rear view mirrors that will let you even look outside the passenger window.
Do you have HID lights yet?
ScienceofSpeed aluminum door handles also look nice, especially on a silver car.
Light-weight battery saves some additional weight.
Also, one of the things the NSX with CTSC could use is some kind of cooling system for the engine bay. I've heard that the CTSC will actually loose power if you are reaching really high speeds (like 150+ mph) because the blower generates so much additional heat it starts loosing its effect when running for longer periods of time.