Yeah, I guess it all comes down to what you're looking for.
When it comes to the "I" and "E" part of the I/H/E modification, it's pretty much agreed that the actual gains are nil and the the purpose for doing those two upgrades are mostly aesthetic in nature. People swap out the factory air box because a XYZ intake sounds cool...and as Ken points out, that's fine.
It does seem that the pre-97 cars benefit more from headers and exhaust but it's still just on the order of 10-15 horsepower or a 5% improvement for $2K or thereabouts.
I did a search on "headers" and found that the improvement might not be all that significant. In the following thread, dswartz had less impressive times with his I/H/E upgrade than he had with the stock setup. Of course, there might have been other variables.
http://www.nsxprime.com/ubb/Forum1/HTML/001281.html
However, I really don't think anyone's proven or even simply shown that headers or headers/exhaust will make any NSX "actually a LOT faster."
I'm not one who gives a one whit about "perception." My recommendation on the short gears had really nothing to do with performance or perception. It had to do with real, actual and tangible driveability issues. Unfortunately, there's no real metrics to illustrate how much better the 1-2 shift is with the short gears. Although perhaps that big BOG of a black hole that disappears with the short gears is a "perception" issue.
Perhaps the answer is this...
If you're concerned about real performance in a pre-97 NSX, install headers and possibly the exhaust. It's about the only affordable performance mod that's less than $5K you can make other than nitrous.
If you're also concerned about driveability, making your car more enjoyable to drive and also interested in gaining a bit more additional performance, install the short gears and a lower R&P (i.e. 4.23 or 4.55).
If you have a 97 NSX with a six speed, ignore all this and if you need more performance go the forced induction route.
-Jim
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1992 NSX Red/Blk 5 spd #0330
1991 NSX Blk/Blk Auto #3070 (Sold)
1974 Vette 454 4 spd Wht/Blk
Looking for 76-79 Honda Accords