I don't know if it's just because I'm a potato, but so far (with the possible exception of the vodyani) I haven't really noticed population doing that much. Sure it's +1 science here, +1 dust there, but overall it feels like population doesn't actually do anything. Everything is either a flat bonus (+5, +10 per X planet) or is so small that it's not worth building unless there's multiple planets in the system that benefit from it (the +1 per pop, +3 per pop if X). In short, my empire feels like it's flat and lifeless, which is a shame because the Galaxy itself feels like its so full of life. 

Comparing it to ES 1 (which I would prefere to do, rather than EL as I know it better) population actually felt important as you got the majority of the income from your pop, rather than just having another planet increasing your flat bonus. Right now the most I care about my population is going "you little s**** better not waste 500 of my influence because you like to flip flop". I don't know if it's just because what we're looking at is the EA or if this is the final way that pop is going to work but I really hope that it's going to change because it bleeds a lot of the life out of the game which I would otherwise love.

*edit I am indeed a potato

When you look at a planet in a system that's uncolonized, the values above it are what you'll receive per population on that planet, in addition to their bonuses. That's why the planets with like 10 pop are shown as producing an absurd amount of resources, because each pop is producing 10% of that total (approximately). System upgrades are factored in the left panel, but everything you see above your colonized planets is produced by your populations.

Edit for clarity:
When you ask about the importance of populations, do you mean of different specific races, or do you mean of having a higher population?

vahouth wrote:

You forgot that your population is the major factor in deciding your ruling party.

I didn't forget that (and for the most part I've managed to break my pops, militaristic lumeris majority when they're about 97% of my empire?) because usually that just serves to annoy the piss out of me by making me waste influence when that party that I thought would get 70-80% of the votes somehow manages to get 5% and then I lose all the laws I put into effect.

When you look at a planet in a system that's uncolonized, the values above it are what you'll receive per population on that planet, in addition to their bonuses.

That was what I missed. For some reason I thought it was only the values on the pop card, rather than the planet effecting it. I really must have been tired yesterday, thanks.

*edit*

When you ask about the importance of populations, do you mean of different specific races, or do you mean of having a higher population?

Mostly the second. The different races seem like it would be interesting, but there's not enough mechanics in the game to figure out what that's like.