Druids’ mistletoe requirement for maintaining good energy regeneration should scale up as they gain more levels rather than being a fixed amount, because as soon as you have that fixed amount there’s no reason to find any more.

One proposed formula is: energy regeneration is halved if you possess less mistletoe than your XL, regular if you have mistletoe equal to your XL, and increased if you have more mistletoe than your XL, possibly with some exception for very low level Druids.