My take on NSX values is we have two distinct markets now.
The first is the highly modified NSX's and they seem to appeal to a younger buyer.
Unless the original oem parts are available with the car, I think the collector value of these cars is gone.
The prices they sell for doesn't seem to reflect the cost of the modifications.
Perhaps the market for these cars is smaller and so less demand equals a price that is close to unmodified examples.
The second market is for stock or near stock units.
These seem to be appreciating as the supply is diminishing as cars are modded and move to the first market or cars are written off for accidents and the like.
I think stock or near stock units appeal to a larger range of buyers, those who want an oem unit that has been well looked after or those who want a stock starting point for their own modifications.
Right or wrong it seems there is more comfort to a buyer of a stock unit, that he/she feels has not be abused or thrashed.
A stock/near stock NSX in my mind is undervalued.
There is no mid-engined sports car that offers as much engineering, reliability and handling as our NSX's.
If an NSX had a Ferrari badge I believe it would sell for considerably more than today.
The Honda marque just doesn't have the value attached to it that Ferrari/Lamborghini have regardless of the benefits the NSX has over the others.
The image of the highly modified NSX's as a young fast and furious type driver's car almost seems to detract from the overall NSX value.
Nonetheless down the road as the supply of stock/near stock NSX's continues to dwindle I would see them continuing to appreciate nicely.