For some reason, I remembered an old Pyramid article today--during the HTML version--and was wondering if anyone ever used it. In short, it was the idea of making mana a limited resource (herbs, rocks, mana organs, water from a magic spring, etc.) that had to be harvested, carried, and consumed to power any magic. You don't recover magical energy. You went out and dug it up.
Just found it,
available as a sample. I misremembered some details, it looks like.