Since there is a lot of discussion about the now quite small contribution of population to the base production I have a suggestion: why not go back to and old, but nonetheless viable system? That is, require population to build improvements: 1 pop for basic buildings, more pop for advanced and special buildings. If there is not enough pop then the pop is distributed evenly between the existing buildings (e. g. if you have three buildings with pop requirement 1, 2, 1 and you have 3 pop then the buildings with requirment 1 get 0.75 pop and the one with requirement 2 gets 1.5 pop). Improvements working with reduced pop lose their efficiency linearly (meaning a building with 0.75 instead of the required 1 pop operates with only 75% output).
If there is more pop than improvements then you have unemployment and therefore morale loss.
Of course that would need a lot of rebalancing. I would suggest to get rid of the percentual bonuses of factories and the like and of base production (but the latter is not mandatory). Just let a basic factory produce 1 production point at full (1) pop. Adjacencies still work, a Space Elevator surrounded by 4 factories would get a bonus of 4 production, giving in turn +1 production to all factories. To make it different from a simple factory a building like a Space Elevator would have to have a higher benefit like 5 base production at 3 pop requirement. But since their function as hub is reduced in such a system it would be great to give them the ability to profit more from adjacencies, like they get 1.5 points from an improvement that normally gives only 1 point production adjacency bonus.
@Stardock: If that is an idea that appeals to you I would happily provide a thorough design document 
(although my job would limit my time for that quite substiantially, but then I would have to refrain from reading and contributing to the forum so much and from playing )
