Form over function I suppose.
Most of the C5 and C4 community that I've talked to
in my years have a serious dis-taste for wings/spoilers.
There is no disputing that the 'right' wing can be an asset
to a car(even the hideous ones on the import rides

).
The point is how often are you at those speeds and more
importantly for how long...? i.e. 'sustained speed'.
For the average 'Joe'. Not much value. Better to speed that
money on other mods. For guys that frequently take the
car on real race tracks, then I could see, and HAVE seen
some guys run wings, I just wouldn't want it on a daily
driver Corvette. Weekend race-prepped car only, sure.
I've participated in a few 'track day' event's at Sebring and
Road Atlanta, and was lucky enough to drive a C5 with
the Greenwood C5 wing, and trust me when you hit about
80mph the car just plants itself to the ground. You can
definitely feel the push in the rear.