[JThur]

I would say a planet is where your population grow.

Resources is something you should be able to get from various sources. Shipwrecks, moons, asteroids etc.

Personally I'd like to be able to get resources from places without having to colonize them.

Food shouldn't be that hard to get. Growing food on ships, space stations or other places would be a nice feature.

If you have the level of detail for individual buildings on planets the scope of the game would have to be downscaled. Not something i'd like.