adding features that aren't really related to the game(ghosts and all) is not necessary, games don't need all of that to be scary, they just need to make good use of elements
adding real horror to nmrih would be simple because the people who play this game aren't really expecting a scary game, and surprises is really what scares people
for example, when i played dead space, i constantly awaited for something to jump in my face and try to make me shit myself, and by doing that, i didn't get one scare in the entire game
however, in the ravenholm map in half life 2, i got some scares, even though the zombies weren't really scary, and i had a lot of ammo and guns, i simply wasn't expecting anything scary, i was just waiting for a random action scene with zombies, and maybe that's what nmrih players are expecting as well
also, Amnesia works differently, it is made to rape anyone who plays games like dead space always expecting something (like me), because it makes you absolutely sure something is going to jump at any second, but it doesn't, and it keeps repeating that until you are mentally exhausted, and then it scares the shit out of you
tl:dr version:
Make players think they are secure when they're actually not