I like the idea of clicking to counteract a draining bar, since it makes the end-goal obvious from the start and visually fills up.
I wonder if it would be helpful to have the hunger depend more on fullness, like hunger = k * fullness, That way the bar doesn't drain at the start, but it drains faster as you get more upgrades. This might also help you tune the scaling, since progress would balance at fullness = hunger / k = (planet_size * clickers ) / k.
Fully balancing it out might be too much for a jam, and I just hand-tuned everything in my entry.