Not really. You haveto apply things a bit differently from car to car, but their's no reason you shouldn't benefit from seat time in any car.
Since the miata is 50/50 weight distribution and a very well balanced car, it responds to you inputs perfectly. NSX is a very balanced car, has a bit more polar energy in the rear of the car from the engine being behind you, so you should easily be able to gain from tracking a miata.
Here I am agreeing with Stuntman again and I don't even know him. Anyway, a car like a Miata gives you a cheap tool for learning to drive. That was the point. Learning has nothing to do with going fast, per se.
In fact, cars with more power are harder to learn to drive. This is because the high power leads to high speeds and lots of passing other cars and maybe toasting your brakes, etc, etc. Cars that are slower, where the whole time you are thinking that you need to speed up... that is the feeling you want when you are trying to learn to drive.
The thoughts you want in your mind when learning to drive are:
o I need to exit this turn faster
o I'll never catch up on the straights unless I exit the turn faster
o my only chance to catch up is in braking and in the turns
o when I do the turn *this* way I gain on him
o when I mess up the turn, I lose ground
When you are thinking thoughts like these, your mind will free to be "in the moment" at the right time and you'll naturally tend to learn the right line and what works and what doesn't. You'll also, likely, notice that nothing happens on the straightaway... other than everyone just floors it and waits for the next braking zone.
These are the ways of learning to drive.
Low power cars, with good balance - are how to ensure you'll be in "this" zone. The Miata is also cheap which is a big plus.
The bad "zone" (for learning), on the other hand, is the "my car is faster than yours so I *should* be faster than you." Fear leads to anger. Anger leads to hate... these are not the ways of people who learn to be good drivers.
$0.02