We could remove all the V8's being one idea, or adding a v10 is also one. As for making rich people overpowered, I don't think so. There's luck involved, so you can get very unlucky. Most of the people are here rich anyways, so the money isn't a problem. Having 10-25% armour won't really be game chancing, but allow you to take bit more beating.
Imagine having to buy around 10 Super gt's in order to get enough parts to craft one V8 in your vehicle. To another player, it might be 15 Super GT's in order to make V8. It depends a bit on luck, but it would make V8's price way better. This would also make groups like TMH have a good role selling those vehicles (they'd raise in price, since you cannot straight off buy them from mod shop)
Not to mention, I don't think rich players mind having to spend more cash on stuff that would be worth while to get. If you want to buy straight V8 Car, you could contact another player who has already make a car with V8 (So basically he could use 10 super gt's, pay around 70mil for V8 car and sell it for 80mil as example, to get some profit, as the v8 would have more value as it cannot be straight off bought)