I always use Kelly Bluebook as a guide. I'll look at the lowest price the dealer would pay on a trade-in for one, in this case, it would be somewhere $47k-49k for one in excellent condition with 52k miles. Then compare that to what the dealer would try to sell it for, which would be $58k. Then normally I would split the difference.
So the dealer wants $57.9k for it, which is where Kelly Bluebook puts the value at. Now the car is Imola Orange Pearl, which is probably the most rarest color NSX but it's a "I Love it" or "I Hate it" color. Many say they hate the color but may not have ever seen Imola Orange Pearl in person. Most everyone who has seen my car loves this color
If you really love the color, then negotiate with them. I think it may go down to $53k or so if it sits there for a while. 52k miles sounds high (If this NSX had ony 15k miles on it, he would be asking $61k for it). But isn't there a doc in Los Angeles who has over 240k miles on his and it still runs great.
You may not see another Imola Orange Pearl NSX around for sale for a long time. In California where there's hundreds of NSXs there's probably at most 6 or 7.