Not sure what will happen with the Supra, but I have unexpectedly noticed mk2 16v Golf GTI's are fetching upto £4500 in stock trim. Same kinda story with E30 3-series, Corrado's etc.
I'd like to think that for its time, and given its competion, the mkiv is more of an iconic Jap car than a 3000gto, 300zx, any skyline, any scooby, or any lancer. At the moment you seem to be able to get hold of a TT for under £4k, and an n/a for silly money. I guess this is a good thing as it offers up the opportunity for more and more Supra's to be abused and killed by chavs, in-turn making these cars harder to come by in pristine condition.
I guess its the same with any car though, if you keep it in immaculate condition and mechanically sound, someone will pay over the odds for it if its what they really want.
....but then again, i'm never selling mine so I dont really give a sh*t!