Roush, Saleen, etc. do depreciate pretty fast, I will give you that. That's why I suggested to the thread starter that he buy a USED Roush. As for rarity, it depends on how you want to look at it. If you group Roushes in with all other Mustangs then they are certainly not rare. Since they do go through their own factory and get their own build number many consider them separate (maybe wishful thinking.) The Classic discussed above is 1 of 50 ever made. As for Stage 3's there have been less than 300. While driving one, you don't see too many cars just like yours driving around so they do get noticed. And that's half the point of having a rare car (money would be the other; but I already mentioned that
).
The argument that you can buy car X, modify it, and beat car Y is an old one and has some merit. Yes, it's a cheap way to compete with more expensive cars and us Mustang owners have done it for decades. However, there are always downfalls: there's no guarantee on the final results of your modding, there's no warranty, you never have the prestige of car Y. Yes, a Cobra owner could take the $10K difference between his car and mine and dump it into
suspension and brakes and keep up with me. Heck, he might even beat me. But, that wouldn't prove a thing. There's more to a car than just the performance aspect. At the end of the day, I would rather drive home a Roush and I would bet the Cobra owner feels the same way about his Cobra.