Well we could have the amount of pop affect how much research costs or how long it takes to reasearch something. It could affect how fast ships are built. culture rates could be affected. I wished there were infrastuctures you could build on planets such as research academies or factories like in turn based strategies. Then pop could play a role in all that.

The infrastructure part is something I also think this game needs. Also, the research costs/speed could be implemented, as a developed planet would usually have a highly educated people(think about todays countries, with the "smartest" being the developed world such as W.Europe, N.America, Japan, S.Korea etc...). Think about the future, whole planets just dedicated to a certain area of specialty(be it agricultural, manufactured goods, war machines, etc...) but all of that they could probably include in the sequel or add-on to the game Sins of a Solar Empire.