I would love to see more flavor around the planets and my overall empire. For example, if I'm human and conquer an alien planet, what percent of my population is human vs alien? What percent is my empire's culture vs the one next door? And how does this change over time as people migrate around the planets?
Also... What impacts do these mixes have on production, civil disobedience, etc? Perhaps multi-cultural planets have better research, but mono-cultural planets have lower unrest.
And can I influence these rates through policies or the local dominant political party? Maybe I can encourage multi-culturalism through civil rights programs, or maybe I can discourage aliens from living on my planets by creating different citizenship classes.
But if nothing else, more stats on literacy, racial composition, lifespan, etc... even if they have no gameplay impact, they're very fun for the imagination.