First of all, I like to discuss a higher difficulty (theme of the thread and my thoughts):
Josh says it all I guess.
Do you think limited gold is an interesting feature? I think it works well in Fallout & TES games. Though, the only thing it affects is early game really (tends to be a slower early game). But I also think that if it is balanced properly (combined with a harsher and harder economy) it could make the game more difficult for a harder difficulty experience.
I played an interesting immersive mod for Baldur's Gate, it made the "Iron Crisis" more authentic to the story as well as items broke more easily as well. A Short Sword cost like 150 gold, and sold for maybe 10. In the original experience you buy a Short Sword for maybe 5 gold and sell it for like 2.
High Level Loot:
Likewise, I think that if some High-Level Loot is not available, or loot in general is scarce across the game, it'd make the game more difficult as well.
Combine Limited Gold, High Cost Items, Less Loot Drops or Unavailable Loot Placements, and you get a more difficult experience.