Well, of course the first thing to mention is that many people have a personal preference. Some people prefer an all black interior, and some people prefer a lighter color interior. So asking whether one is better is like asking what is someone's favorite color in order to decide your own, if you know what I mean.
FWIW, I prefer my ivory interior. Black is too dark and gloomy - for my taste. If I had the choice, I would choose the tan/camel available in '94 and later cars, because it looks like natural leather. So anyway, that is MY taste.
I think the condition of the interior is very important, and for many, may be a more important consideration than the color. Any color interior may be well cared for or poorly cared for. I take care of my leather interior using Zymol Treat, which contains collagens, the fatty substances that are present naturally in genuine leather and give it a soft and supple feel. The big problem areas to look for on a leather interior are the suppleness of the leather, the cleanliness (if it looks dirty, it is), and most of all, the side bolsters, particularly the driver-seat left-side bolster which is subject to wearing through if the owner is not careful and slides over it every time he gets in and out of the car. There are various ways of dealing with bolster wear (if you're interested, see the FAQ and do a search on the forums) but it's even better if you can find a car that doesn't have severe bolster wear.
Of course, one other cleaning issue is that black hides dirt better than ivory does. I know some people who even use black floor mats with the ivory interior. However, I love the lighter "look", and IMO floor mats are there to get dirty and get cleaned again. If I had my choice, I would have preferred that even more of my interior be ivory rather than black, including the interior panel behind the seats (black in all '91-93 cars regardless of interior color, but color-coordinated to the interior beginning in '94) and the gathered leather on the interior door panel (black on all U.S. cars, but color-coordinated in some foreign markets).
I don't think there is any significant difference in market value because of the interior color of any NSX. The only exception might be the color-coordinated interiors (orange, blue, etc) which were introduced in 2002, but I haven't heard anything, even anecdotal evidence, to indicate whether those colors might fetch a premium or a discount vs the traditional black or tan or ivory.
HTH
