Having played Cardalaxy a couple dozen times, now, I've noticed something about the current Wellness mechanic.
Once the player has reached the first Wellness milestone, the Wellness decay mechanic pressures the player into investing heavily into Wellness to stay ahead of the decay. Unlocking Health Tracking Centers and/or Modular Farms becomes a major survival priority for the player, as a result. However, once either of those are unlocked, it becomes much easier to overshoot the Wellness decay and jump straight to victory.
I therefore suggest two changes:
1) Currently, the rate of decay is a function of the highest Wellness the player has ever reached. Change this to instead be a function of the player's current Wellness; as Wellness drops, Wellness decay should also drop.
2A) Double the Wellness amounts required for all milestones OR...
2B) ...add more Wellness milestones such that Victory is still the last milestone, but requires 100 Wellness.