Why is the population increase cap set at 2 million? That seems a little low. There should be at least some room for incremental increases due to good morale, and also the racial bonuses. Right now I'm not seeing much of a difference between a growth rate of 45% approval, and 75% approval, aphrodisiac with univeralists and whatever the highest pop option is. The cap should at least be set high enough that there's a difference between having those things and not.
I think players should be allowed to dig their own graves in overpopulation, it should make interesting strategies with cultural dominance, and small planets.