Pulling up the shadows with Premiere Pro introduces a lot of ugly noise that's hanging out down there, so I've gotten the trial of AE to see if the noise reduction effect will work for the shadows, and it doesn't look very good. fine detail is obliterated with that effect. Perhaps some sort of Super resolution effect would work.
Purely hypothetically, if the original grain plate which was used for the Blu-ray was found, would it be possible to cancel out the grain?