I agree w/ nsxsupra in that the most desireable combo will be 97-01 NA2's, for a few reasons:
* Most hardcore lovers fell in love with the pop-up headlights
* More powerful engine
* Available in targas too
In all collectibles market, prices are determined by supply and demand, and if we look at the demand side, you're looking at the collector. Once you define this collector, you'll define the criteria these collectors of looking for, and hence the type of NSX. I surmise that collectors will be more or less purists who fell in love with the NSX from the very beginning (ie pop-up headlights), enjoy a spirited drive (more powerful engine).
The collectibles world is driven by nostalgia. Given that most NSX's sold were pop-up headlights, you can be sure collectors will always fall back on this nostalgic factor.