For what it's worth...the only thing i think a purpose bred gun dog of any type has over a lurcher is it's nose..yes they have better noses but purpose bred gun dog's are of little use for anything else other than working to the gun of some sort.
On the other hand a lurcher especialy one with a good lump of collie blood in it can do a hell of a lot more and a one with a good coat will take just as much bad weather as any other dog..
You can go shooting/bushing/lamping/ratting/ferreting the list is endless for what you can do with a good lurcher..but i have found purpose bred gun dog's limmit