They are worth whatever a buyer is willing to pay. I love NSR's and think that they should be worth a lot more than they are sold for.
At the same time, if you ask an rgv or tzr owner the same question you will probably get the same answer.
I guess if you are looking to buy a 2t road bike you will most likely end up with an rgv. They are everywhere and are cheap as cow poo in paddock. If you have class and style you will end up with an NSR. If you see a tzr for sale, you may buy it or you may not, just depends how much spare time you have to find parts and repair it.
I would try to sell it for an amount that I felt comfortable with. Don't rip yourself off, but understand that it's not a gp championship winning collectable. Start at a good amount as they are an NSR and lower your price with urgency.
Personally I hope you get $50,000. After all they are the greatest bike of all time.
That's what I think anyway.
Andy
Bandit7