I don't think so for the simple reason that those "modern sensible-power coupes" are in a completly different league. The Supra is in the non-sensible category.
Let's take the BMW 850: you can have it for peanuts but boy oh boy: don't ask
500 HP from it or you will have to carry peanuts by the shipload.A 928 GT (S)? Yes, but you will need a compressor on it. The compressor kit alone will set you back 10 kUKP and even then 500 HP is far from certain.
The BMW 330 bi-turbo, of which we spoke recently in this newsgroup, even the Alpinas and some tuned Hartge's: does it compare, does even an M3 of M5 compare to the Supra? The M6 would: you can wait an other 10-15 years before that's in the 10000 UKP range (and once you buy it, be sure to have another 10k ready to engage).
The Supra keeps its price because basicly it is a very strong, overengineered yet simple car with an engine which used to live in a truck and a unbustable gearbox. Standard 330 HP, mildly tuned and without affecting reliability = 500 HP, possible 800HP if you really want it...
Something similar and existing will get you looking at a car with "Ruf" on it: then you need the 10 kUKP as first payment or cover the fix of the gearbox after 50.000 km...
The Supra has found its niche, has its followers and its price has stabilised: price will never go down- expect them to go up-: the car is kept in shape (and keeps its value) or it's scrapped for parts.
Same story goes for the BMW E30, Cosworth's, Lotus Omega etc... A BMW M5 goes down in price, the Lotus Omega doesn't.
Tom De Moor