Well, that's what they keep adding content for: to keep the spooks fresh in new updates. I don't think it would be any more entertaining if we could defend ourselves against something is all. It would likely be the same scenario where, if you've seen all the horror, you've seen all the threats kind of thing. Either way, the horror wouldn't last long.
Why I bring all of this up is because I believe this is the direction the dev wants the game to go in, as evidenced by the tease of a rifle at one of the radars, and an alien gun that we can't quite use. I think they want us to feel helpless against the aliens. You see something like a tripod, and you really think we can defend against that? You know, that kind of thing. Perhaps against creatures like the Creepers, sure, but defense can only go so far, unless they add more in the future with the focus on said mechanics.