I think Trophy prices will level out and always command a premium (Over other RS Clio's) - but it doesn't have the cult status and following of say, the Williams - that is, they certainly won't appreciate. With the Williams there were only 2 sports models - Williams, which there were approx 1,000 (330 or so of each run, 1,2,3) and the valvers & neither were mass produced (Most have now rusted away or been wrote off) and both rated as a true great drivers cars (1*2, better cars, not better drivers cars), I think the only Clio which will go up, and has done to some extent are the Williams.
The newer RS Clio's there is the 172, 172 Exclusive, 172 ph2, 172 Cup, 182, 182 with Cup packs, 182 Cup, 182 Trophy - aside from the original 172 ph1's, those other 6 variants are almost identical bar wheels, seats, exhausts (I'm sure there are more differences, but please, don't be too pedantic) - neither is any quicker than the other - where there is soo much choice and lack of differentiation, prices are only going one way and I deffo think of late they have fallen.
The reason that no one wants that Trophy is is the suspension - if it put the sach's back on it would sell.
I also think a reasonable priced Trophy is now 'about' £6k. I think if you're not using it much, in a couple of years and it's mint, it will be worth about £5k - I can't personally see it becoming a 'collectors' car, but think prices will stay a little more afloat and if you're not modding it, or doing 50,000 miles a week in it, they won't come down too much.
I had agreed a price of £6,400 with mine recently, from purchase I have spent a good few k on it, but it only cost me £6,700 two years ago - that's pretty good and I hadn't lost too much, but I decided to keep it - as I'm a bit annoying and can never make up my mind.
Bit of a rambling post - sorry.