Just something on the side, referring back to the treasure maps thread idea I made a while ago, perhaps you could introduce a quest with the reward being the tools to read these maps? such as a compass, sextant etc. so that is possibly something.
On the other hand, the Hera hearts idea was a great suggestion, but ofc there should be tougher baddies to kill to 'balance' this, which itself is a reward also (the ability to kill tougher more skilled baddies would create enjoyment for players!)