Winston did have his own purpose in the movie and I know it didn't seem as big as the rest of the GBs, but it raises the question “would it be the same without Winston?” I think that answer to that one would be no. He had the view of everyone else out there that was hearing about these guys running around and catching ghosts, and because of that he was the level headed one. He even got the last line of GB1 (if I'm right and unless you count Louis' “Does anybody wanna interview me? I wanna go with them, in the car..” which you don't really hear). So to me and pretty much everyone else here (I think), Winston is on the same level of importance as Egon, Peter, and Ray.