Is that necessarily bad, though? It WOULD seem like a colony would ultimately evolve towards some final pattern: You start a colony to harvest the resources of that planet. When those resources are depleted, you either end up with another urban center that now must import the raw materials of even newer colonies, or an abandoned planet.
It's like a city on it's ultimate sstate requires lots of resources, requires lots of attention and also care.
While you may end up with one or two cities like that, it's not reasonable to have all cities end up like that. Like you said cities need resources, they explore what they have and then start using the resources of newer cities.
If all we have is great colonies full of people requiring resources like mad then your empire would fall or would have to spend all your money trading in those resources.
In the end some cities have to be different, otherwise you won't be able to stabilize your empire.
On Master of Orion 2 for example you have colonies full of scientists, others full of farmers and others full of workers.
The difference is that there you can change the colony type from a research colony to a production colony in one turn and without consequences.
There the same population that can produce food can also research.
Here research colonies won't need billions of scientists, it requires less population but more infrastructure to reach the same level of efficiency than a farm colony, for example.
In the end we want the transition to be part of the game experience instead of a quick decision of ether I want more food or research that turn.
Maybe, maybe not. People do all ultimately need and want similar things, so all colonies would have the same needs. How effectively they meet their needs, or the needs of other colonies, depends on the local resources. Presumably, there's a finite amount of resources that could be mined from the planet, after which the planet has to grow beyond resource extraction to become some manner of urban center, or be abandoned. This is what happens with cities in real life, too: A town is established around some kind of mining operation, eventually the place is mined out, and either the town evolves beyond the original settlers' intent, or it dies as everyone buggers off for greener pastures. If it doesn't die, the resulting city ultimately ends up fairly similar to every other city.
People have similar basic needs, a colony dedicated to research will have very different needs than a colony dedicated to farming.
One you can have small biomes scattered across the world filled with high tech machinery and equipment, while the other you have to terraform as much as possible the surface and you will end up full of villages and cities that will grow more and more with time.
