Well… There are some things you SHOULD upgrade. Like the front suspension in the Mustang. Of course that 10,000 it’s not only suspension upgrades, there are also some engine mods and some security stuff. ** And it’s still cheap. **
$20,000 car + $10,000 in mods = a $30,000 car with 400 HP with amazing agility in corners.
Anyway, the REALLY problem here with the muscle cars is that there are a lot of douchebags driving them. It doesn’t matter if you drive a ricer Civic or a top-end Koenigsegg if you are bad at driving you will always lose.