you can NEVER have too many cosplays.
Of course, if you find you've been avoiding wearing a particular one for a couple of years, you might as well sell it or give it away to someone who will wear it. Also, once you get over a certain number of cosplays, you'll find you're running out of room in your closets and will have to get rid of the older ones to make room for all the new ones you make.
I think I've made almost 200 costumes now... not sure exactly how many I've got at home, but I do remember one time I'd listed all of them.