It's not a stupid question - this really should be visible in the game. Population = more raw production (not to be confused with manufacture). 

Raw production = (pop^0.7)*2

5pop = 6.1 prod

10pop = 10 prod (when it breaks even)

20pop = 16.2 prod

30pop = 21.6 prod

Because you get 5 production base from the colony capital building AND population costs happiness, I would strongly recommend that you minimize happiness buildings and then build farms until you reach your happiness cap, but other than that focus on % modifiers as those will pay off much faster.

Raw production is.. just that.

The difference in production, assuming 100% governance focus on manufacturing, from a pop 10 to pop 20 planet:

6.2 raw production difference, assuming 100% morale (25% production bonus) becomes 6.2*1.25 = 7.75.

With 400% manufacture bonus from buildings, that would then becomes 7.75*4 = 31 manufacture (or research, or wealth) difference. 

This is without taking economy star bases into account, each one gives another 10% raw production modifier.