If I were going for a Spyder I would insist on the carbon bucket seats. Though they were standard, so many appear to have been sold with the no cost option of comfort seats and they are just not as special as the real deal.
As the rearward visibility is not great and you will at some point have to park it with the hood up, so I'd also want the parking sensors.
Personally i'd want one with a/c too, as it makes a hell of a difference to keeping the screen clear on non-dry days and on hot days, a/c is essential.
Other than that, a manual would be nice (though i found the short shift to be rather stiff on the one I tried) or if its is a PDK car, then find one with paddles rather than the steering wheel buttons (unless you happen to like them of course).
Lastly - and this is very personal, i think they look best in white!