So sorry for talking up so many of the latest posts box, but my brain doesn't want to stop thinking of ideas.
I think we should add in semi-invisible ghost npc's that float around Hogwarts minding their own business. They would hover a little off the ground. They kind of have chances to randomly appear near players for a couple second maybe around 15. In that time they kind of float around almost robotically. They wouldn't do anything except add to the Hogwart-sy feel.
My idea is much shorter than the other ones I have, but I hope you like it!