I think that there should be a technology branch which allows you to increasingly automate components and planetary facilities so that they require less personnel. For instance, the lowest tier might cut down on requirements by 10% while higher tier would allow huge vessels to essentially be unmanned except for a bridge crew.
Going higher in the tree should unlock an AI technology branch which not only cut down on needed people but also gives a slew of bonuses to research rates, population growth, construction rate, basically everything, but of course going down this path too far could be hazardous for your health
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