depends on the car. eg the lotus seven replicas such as westfield, caterhams etc are far better performance cars than the originals.

also some cars are just too rare to be realistically affordable.

eg the prices of original AC cobras, GT40's etc is horrendous. you need well over a hundred grand for a decent original, some times many times that!! Yet most good quality kit car replicas of cobras and GT40's can be built to handle and drive better than the origianal at a price your average guy can afford. Many such kit cars are considered good cars in thier own rights....