Maybe instead of deleting an incoherent post, you mods can warn the person and create a thread to put those horrible posts in. A "These are examples of horrible posts" thread, or something. It would give people examples of what not to do when posting.
Edit: I just thought of why this wouldn't work. If people can't read the rules, then I doubt they are going to read anything else either. Damn, I was too quick to hit the post reply button.