i go autox with my NSX,
IMO, NSX is a pretty good autox car.....but don't feel bad if you're constantly getting beat by miatas, civics, and other lighter low horsepower car like this.
Not saying the NSX doesn't handle good.....in fact, it handles superb. Its just that lighter cars has more advantage (turns faster) in autox event since autox track are set up really tight....rarely rarely you'll go over 60 mph.
One more thing to keep in mind though, a stock NSX does have a lot of bodyroll when autoxing which kind of hinders the X's performance a bit.....a stiffer swaybar will get rid of the problem.
Also, keep in mind of the tire you're using....if you're serious..i mean really serious about autoxing, I suggest using tires designed for autox....such as Falken Azenis sport or similar tires.
Trust me, having a good set of autox tire will shaved 2 to 3 seconds off your time.
forget about all the performance upgrade.....unless you turbo or supercharge your car.....you will not see any improvement!
P.S. no worries, NSX will keep those miatas, civics ass on the track.........just from my experience