I believe a good example of a any RS Renault will end up an "Iconic" collectable. You only have to look through classic car mags or the retro car publications, a good example of some truly awful cars are fetching decent money. The secret it seems is originality and complete history.
Most people don't consider a 2.0 Opel Manta a classic, but you try and buy one now, I had 3, broke 2 for parts despite them being serviceable. Its all down to perception, the fact that the RS Clios have such a strong following now (just look at the membership of this forum) pretty much assures icon status in the future, and with it a "classic" status. As numbers dwindle through natural wastage, chav ownership and scrappage, prices will start to slowly strengthen, eventually, and it will be a fair time in the future, prices of what remains will rise, thats a definite. They will never be worth daft money, but I assure you that a well kept example will be worth a good price in years to come.
The strongest value will be in limited production run cars so naturally the Trophy, 172 Cup (especially as most will be butchered into track cars) and PH1 (Not limited run as such, but produced in a short run prior to the PH2 release)
Keep it standard, keep it maintained, keep it's history up and keep it. Better still, buy a cracker while they are cheap, stick it in your gently heated and ventilated garage and enjoy it in 15 years time when you can't find one anywhere! clever money would buy a minter from europe and store that, they are mad about cars, Left hookers are more expensive (european second hand car prices are shocking!) I've seen pretty ordinary cars get daft money at european classic events, they're bonkers!
G