As someone who uses WinUAE, Minimigs and real Amigas, all I can say is that you can "feel" the difference between emulation and the genuine article.
It's like asking someone why they want to drive a 1960's Jaguar instead of a 2011 model, when the new model is just so much faster and comfortable. 
I agree but at the same time... I think that I would actually prefer WinUAE than spending that amount of money on it. Also the NG amigas feals just as much Amiga as my a4k does.