It's not a black-or-white type of question. I haven't had a screen protector on my Nexus (on any of them, for that matter) at any time, and my screen is scratch-free. Your results will vary from anybody else on this forum simply because you don't do the same things they do.
If you're worried about it and you don't have any problem using one (some people dislike the texture), I would say definitely go for it.