I've done the banshee thing in the forest a few times. One game I had found 5 scrolls of danger. I put two in a safe place, and then cursed and read the others. There was a noticeable change in the stuff that dropped. Still, I never got anything too fabulous. Endless potions, arrows, etc., though. I don't remember the Banshee being too powerful. She would occasionally hit me when I was picking up stuff, but I could always teleport away. Forgetting where I left her, and returning and not remembering ears wax, was a bigger problem.