If we continue on the path we're on, then the most you can do with any individual planet is to make a few building choices to fill the slots, pick a focus, and then let it alone.
Is that a bad thing considering the number of planets to manipulate at end game?
To recap, each planet has:
* The resource meters (Farming, Mining, etc. etc.) governing the number of resources generated per city/population unit
* Focus, which effects the resource meters
* Health meter (or Growth meter) governing the rate of growth
* Enviroment "meter" which effects Growth, Farming, and Happiness
* Happiness meter
* Control meter (or Security meter) anti-spy, anti-unrest, cost to change Focus
* Buildings, which among other things effects the various meters
* some sort of Infrastructure growth meter or build queue items
That's a lot of information per planet, and other people have proposed three times as many meters.
Combining infrastructure with pop doesn't have to destroy the all information contained by infrastructure. There could be (based on Happiness vs. Control perhaps) unruly cities/population units that eat Food but produce little or nothing. There could also be "cities" that no longer have much of a population: "Ruins" that produce nothing and don't eat food, but can quickly grow back into functioning parts of the planet economy. Unrest simulates not having enough Infra; Ruins simulate having too much (as in PC's biobomb idea). There could be a "third world" type class to to directly indicate lots of population without infrastructure--but personally I think Unrest covers that situation.
In addition, as in Civ/moo2, buildings represent a certain amount of infra. If there is an area-of-effect superfarm in the starsystem, a bonus to the Farm meter to nearby planets represents the RIO the empire recieves from completing an infra project.