I did the 18/19 RPM rims and they are arguably a very heavy setup... But with that I feel came some durability in that I haven't had any problems bending them, etc... and we do have a good amount of construction pot holes still down here in FL.... so they have taken some good hits. Plus I am lowered with Bilsteins & Dali springs, which is definitely much firmer than stock. Performance wise I added headers around the same time, and feel it was probably a wash performance wise with the wheels in the equation. Cornering & handling wise the car feels flat and planted on the road... With the shorter sidewall however as all know, you probably are giving up some predictability of feeling the limit of adhesion coming on... If you track the car definitely go 17/18. I don't track my NSX, and they made street racing a felony in FL, which kind of took the fun out of it for me... so without much need for stoplight dragraces, I have been very happy with the 18/19, and you can't beat the looks. Which was the point anyway. And if you dig on compliments, you will definitely get them with chrome 18/19s.... And it helped shave 10yrs off how old people think the car is... I guess everyone has a reason for his/her NSX.. For me its the great handling AND the looks.. the balance. My previous M3 had the handling but didn't do much for you when you were sitting still. The NSX has the exotic looks with the plus of very good handling... and I wanted that balance.. If I were going to track a car, I would have kept my M3... If you want to 'feel' like you are in an exotic car then the NSX is the way to go... and with that said, the 18/19s are a great part of the package...
Short answer: 18/19s are for looks.