You only get the one chance to loot Kistandalius' back room (re-load if you have a recent save to try again). You may be able to access the chest with Telekinesis, assuming it is not locked (don't remember).
On hard you get the same experience points, but the monsters are tougher. On normal, I got various bonuses (ie vitality) on the items consistently around Aleroth (leggings in the house with the mirror, swords/bow/shield in George's shop); on hard these items had no bonuses (only the durability varied when re-loading). I didn't notice much of a difference in dropped items, but then I only got to the bottom of the catacombs.
