Nothing wrong with replicas if done properly. Theres a huge difference between a 'replica' and a 'look-a-like' though.
I can see why people do it for insurance purposes or maybe lower running costs etc, but sometimes it can get a bit pointless if you end up spending silly amounts on it with a big engine and everything. When it gets to that stage it would be better and cheaper to get the real thing.
Ive heard of people spending over £10k on escos reps (one i know even £13k!) when they could have the real thing for similar money.