Even fakes can acquire an aura: one collector had a beautiful Paul Klee drawing by her bedside, and learned after many years that it was a fake. It stayed by her bedside, as beloved as ever (if not nearly as valuable). But again, if it had been stolen, she would not have replaced it with a reproduction, or some fake fake.
The point is that so long as authenticity can be determined somehow, the value of an original unique artwork will always be orders of magnitude greater than the value of any copy. It doesn’t matter if you can tell the difference; the value lies in the authenticity, not in the aesthetics of the piece.
That said, advances in reproduction technology have changed what artists do, in profound and interesting ways. (from a September 2013 Reuters Report)