Paying for two sites

No, it's rude. You are potentially preventing someone else from camping. It doesn't matter if the cg likes it or not. If you want privacy, then find another campground or boondock. Goes along the same lines as the folks who reserve every weekend at some campgrounds and then just show up when they can. It's very self-centered and disrespectful of others. What I would consider, however, if you get there and the cg isn't very crowded then possibly purchase the adjoining site at that time.

I don't understand the mindset of doing an activity that by definition brings you into potentially crowded conditions, then demanding no one be near you. Buy a cabin in the woods.