+1. The main complaint against the NSX within a couple years of its release was its lack of HP compared to its rivals. Anyone whose driven a 500 HP Lambo, Ferrari and a supercharged or turbo NSX will attest to this. The NSX was engineered for more power within reason.
Given the fact that so few NSXs were produced and the undisputed opinion of its significance in automotive history, I believe it should continue increase in value so long as the modifications are to improve it's performance without cutting up the car or sacrificing reliability and installed as if Honda had done it at the factory. I just recently had the SOS Twins installed in such a way. My car still looks 100% stock because I fell in love with the way the car looked from the factory. To be honest, I didn't buy my car for its collectability or as an investment. But, I still want to stay true to the NSX design. And if it continues to appreciate, that's just icing on the cake.
I have the SOS twins too. I love the setup so far. The packaging is tidy and could pass for OEM since it so clean.