I actually have both a 2009 C6 and a 1991 NSX. Personally, I wasn't super hot on the Corvettes until my boss bought a C6 and let me drive it. After that experience, I realized that GM had upped the ante for the quality was better than the prior versions, however, still is a less than that of the NSX. I also have a S2000 and I thought that GM did some of the same things Honda did with the S. They spent money where it mattered (or least where they thought it mattered) like the drivetrain, brakes and went cheap on some of the interior pieces (ie. I just hate the visors on the C6, radio on the S2000). Yes, the Corvette is inexpensive and depreciates far more than our NSX's, but that's fine with me for I nabbed a nice very low mileage used one for less than what any NA2 NSX goes for.
I use my C6 as a daily driver. It is actually quite comfortable and civil. The plastic body makes me less sensitive to morons who might give me a dingy in the parking lot. Also, parts are silly cheap compared to the NSX. The car makes remarkably good gas mileage and has power that exceeds my abilities to tap safely.
As for exclusivity, the C6 is not the same as the NSX. Heck if you want exclusivity don't bother with the C6. Personally, I'm not into that and don't care. If Honda made 100,000 copies of the NSX, I'd still own one cause they really are gorgeous and quite frankly the world would probably be a prettier place.
Regarding the styling, the NSX in my book wins hands down. The lines are just intoxicating. The C6 is certainly no dog but it doesn't have the same exotic look of the NSX. Rear mid-engined cars have a distinctly more svelte appearance that I seem to be drawn to. Though I will make one point and that is that for some reason, chicks are way more apt to talk to you when you are in a Corvette than a NSX. I don't know why, but I've had a number of chicks ask for rides in the Corvette, but none have asked for one in the NSX. Strange?
In the drivetrain category...well, the C6 is newer and just has gobs of power and torque. It seems to have power everywhere in the powerband and somehow that thrust makes you forget any of the deficiencies the car may have. Sure it doesn't rev like the NSX or feel as lively as the NSX, but when you've got the pedal down, you really have to hold on cause it will just go!!
In handling, the C6 is pretty good, but, for me, the NSX feels more connected to the road and seems to be more lithe. I haven't tracked my C6, but those who have praise its ability. What limits I've tested, I think they are likely correct.
Having disassembled both vehicles to some degree, I will agree with everyone else, the NSX is just engineered to higher standard and put together with care and an extreme attention to detail. The C6, though, is one of the better American made cars and really isn't as bad as some make it out to be.
In the category of reliability, I believe my perspective is skewed for my 1991 has reached the age where it needs a lot of preventive maintenance and repair of failed parts (due to age). My C6 is much newer and so far has been quite good (knockin on wood). So overall, I've spent more in maintenance on the 1991 than on the C6. Also, since the C6 shares components with a number of GM vehicles some of the parts are silly cheap and easy to find.
So would I have bought the C6 if Honda had a new NSX...no. In fact, I believe I will likely get rid of the C6 when the new NSX arrives. I will not get rid of my beloved 1991 NSX (my wife would kill me if I did or have me institutionalized).
Bottom line, if you want a nice daily driver with great performance, you can't go wrong with a C6. The NSX is one of the finest automobile on the road and is in a unique league.