Whilst those ideas are good, i had an alternative use for a planet's population in my
Micromanagement Proposal (the thread is a little dated, its been developed further elsewhere), the concept being that the population is both a source of income and a place of expenditure; income generated from Taxes which were adjustable (hey, it was
micromanagement ) where high taxes give you a short run boost, but low taxes give a long term boost, and expenditure to keep the population from revolting or destroying things on the planet etc. The idea was that this "internal" idea of population could be affected by "external" (ie, how the game is now) events such as structure killers killing people.
Having said all that, the ideas arent mutually exclusive; eg, your idea plus that more people = more taxes, but also more costly infrastructure/security (to counter the paratroopers).
What do you reckon?