shove non stacking buff on something that's always around at the planet, like... Constructors?
you could even make it a Limitless Range Aura, that effects all planets, friend or foe so any constructor in the world, would make sure all planets have this ability to produce crystal/metal.
then planets earn, metal and crystal?
not ideal, but it would work, you could hide the ability in ability 4
but all planets would have identical metal / crystal income!
not sure what removing the crystal and metal extractors would do to the AI tho.