id say any car will eventually become rare over time, its wether you want to keep the car for that long. id say for an st to start going up in value due to its rarity you would have to wait atleast 25 years. if they had only made 500 then the amount of years would come down but even then not by much. look at the escort gti as a comparison as the st is pretty much a focus version of the gti, over shadowed by the focus rs