Buildings linked to population

Loving ES2 at the moment but finding the fact that all systems can be upgraded exactly the same as each other and with all upgrades a bit dull.

Would it not provide a more strategic gameplay element by limiting the number of improvements to the number of population slots on a planet, so you can tailor each planet to what you need and its specific bonuses. Each system also has a small amount of upgrade slots (for upgrades such as interplanetary travel, colony level upgrade) that give system wide bonuses.