No they won't. The Escort is far more iconic than the Saph and hit 'modern classic' status very quickly.

Of course it isn't the best car out there for the money, but none of the RS Fords from before 2000 are really. You could easily spend £4k on an RS Turbo now, and I'm sure there's plenty of better cars out there for that money. And £5/6k for a Saph isn't extreme now, and I'm sure you'd probably get a nice Evo or some such for that money.

But technical ability isn't what it's about. All the RS badged Fords tend to end up with classic/cult status, which means they hold their value. The Escort Cosworth is probably the most well known of them all (with the likes of Clarkson etc still giving them a mention to this day), so it naturally makes values hold.