Perhaps the option could be to have different currency for different upgrades, but I feel if that is the case the game has to be a bit more than just idle, like maybe choosing a path at a crossroads that lead into different creature types and all, maybe a way to lose? Like you can "go on a hunt" for as long as the player survive. Like maybe more like components to craft than currency.
I'll come back to this if you would like, give more feedback when there is updates!