Regarding city generation: there is a vast community who work on landscape and city generation for flight-sims such as FSX or X-Plane.
here one random article taking about the auto-gen of cities in X-Plane:
http://developer.x-plane.com/2012/03/wh ... or-cities/
Flight sims are of the most successful areas where manual editing of terrain features and procedural generation are mixed. (basically populating the whole area of the earth in variable fidelity)
,for use in a realtime 3d engine.
Important here is: the users dont try to let the computer generate "everything", but use a layered approach of combining manual definition of locations and shapes, with manually build structure-templates,
that then get automatically placed and modified by a generator. The quality of the scene gets better and more realistic the more template assets are provided to the system, and the better the algorithms of the generator work.
Another lesson from MS Flight simulator is, that even if the product is quite old, its retaining a large community by being able to be modded and run addons.
Its more of a rich framework that can simulate a world, than an encapsulated "game".
Circling back to Limit theory: I would rather generate ships and stations out of manually editied "prefab modules" than geometric primitives.
Eg: higher fidelity models of elements like trusters, hull segments, wings, cockpits, docking bays etc.. The modules are then connected using some standard seams or connectors, and get adjusted by material and color-scheme, and have some "stretchpoits" to adjust their scale cleanly.
These modules then can also be provided by modders to change and enhance the style.
The results would look better than just connecting metal shaded boxes and planes...