Being such a weird person collecting JUST perfins I have to react on "the stamp with a perfin will have less value than a normal stamp because of the mutilation of the image."
Hmm ... why someone pays a hundred times more e.g. for an Austrian stamp with a special perfin than for a normal one?
It's another - newer - collecting field that has its place in philately already, and if you take a look at
ebay you will see how many people cherish these stamps.