It's just our brain that perceive more details even if in reality isn't there... of course, the DNR should be not overly aggressive...
I tested it with The Arrival, and worked well; plus, I used it in AVP:R shots upscaled from DVD to match the BD grain - and again, it worked well too!
But, for example, with Predator UHE it didn't work so well as in the previous cases... because it's quite hard to squeeze out some details from a wax mask! (^^,)