
You say people wouldn't cross-shop the NSX and XL because the NSX is a track car, then go on to say people will cross shop the 911 with the SL? The Porsche has more in common with the NSX than it does the SL.
People buying any of these cars new are in all likelihood not taking them out to track days anyway. So they're all buying them to be seen in. No reason they wouldn't cross-shop the NSX and the SL when new.
I agree they wouldn't cross-shop the S2000, though...
A Porsche Carrera Cabrio is pretty comparable to the SL. An NSX is not. Just about every car rag has done luxury cabrio comparisons with the cars I listed above (including the Porsche 911).
I'm just saying that they're totally different cars. Sure, people may look at both the NSX and SL...if they have NO idea what they want. If they want a performance car, they'll end up in the NSX. If they want a luxury cruiser, the'll end up in the SL.