While I was thinking about farid and his bunnysuits... I had another thought. "perfect as the stars themselves' he says a lot, but Do these people see stars? Do they have even have a sun? They certainly have a day/night cycle (it could be artificial magics from the Vatican of course), but no matter how thin and wispy the fogs might be, it is going to be effectively opaque at any sort of large distance if the fogs are sort of all encompassing outside the city.
Are the fogs endless in all directions? on one hand, go far enough and assuming you aren't eaten by a grue(oh wait wrong game), you'll probably end up on some random world. But if the paths change, then if the city were to expand, perhaps it would just push the paths out further as well? I very much doubt you could reveal the paths between the worlds by simply pushing the fogs away right?
And then, since crowding is such an issue, why don't they expand the city? I imagine it is the simple result of the Inverse-square law and square-cube law. Doubling the magical energy used to push out the fogs does not result in a doubling of usable area: pushing the fogs away in the 'up' and 'down' directions are not useful directions after a certain point. And whatever method they use for making sparks, pregnancy or otherwise, if it scales linearly with population, and population density remains the same, then there will be a equilibrium where the city simply cant grow any further.
But if there was a 'sky' above the fogs, which did not have to be pushed against, and their spell was a cylinder instead of a sphere, then there should be no reason that they couldn't add another 'quarter' to handle more people. I don't know what you would call a city with 5 quarters, but it is not important.
What I am trying to say is, I think the eternal rome is stuck with very dreary weather 24/7 and the only experience the inhabitants have with 'stars' is from the worlds they originally came from, or the results of the illusionist's guild.
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