This came up as a side topic in my discussion of my first seven years:
Run a campaign that has populations which tolerate ultra-low gravity, i.e. which have a lower G limit of 0.0. At the same time, introduce "mining companies" into the civilian sector who will produce mines and create populations on worlds with high mineral concentrations.
The game-play driver here is to enhance the civilian sector, and to make it a little (or potentially a lot) cheaper to develop a system. At present, most of the bodies in a system can only be mined using automatic mines, which cuts the number of populations (and hence variation in demand for trade goods) a lot. If populations could be established on asteroids and there was commercial sector generation of mines, however, then the civie sector could drive the colonization of the small bodies in a system, which in turn would drive trade with the miners of such civilian sector essentials as "Betelgeuse Girls Gone Wild" DVDs.
Another game play advantage would be that it would give player races something else to spend wealth on. Planetary populations could have demand for TN elements (hence the companies mining them), and you could add a mechanism for a player race to "out-bid" them, i.e. state a price which it will pay for particular minerals at a particular population.
The "cheaper to develop a system aspect" would come from a reduction in the need for automated mines, which at present (at least in my campaigns) consume a huge percentage of the output of factories and greatly slow economic growth.
I can think of three places where the current version of Aurora might have problems:
1) Divide-by-zero problems if the lower end of a populations G rating is 0.0.
2) Terraforming: you shouldn't be able to put an atmosphere on an asteroid.
3) Temperature: there shouldn't be a big difference in colonization cost between an asteroid near the orbit of Mars and one near Jupiter; I would vote that the temperature penalty (at least for worlds that can't take an atmosphere) only apply on the "too hot" side.
Hmmm - item #2 above got me thinking about terraforming. There's probably a nasty formula for just how much gas it takes to create one atmosphere of pressure on a particular world - small worlds should require less, but they also will typically have lower gravity which would require more. I think the current model is ok, since most planets that will be terraformed will be big enough that it's not worth thinking about the complexity, but I remember how much emphasis you put on getting the physics right in your world generation routines. If you want me to think about a formula for a "terraforming difficulty" multiple, i.e. a factor that multiples the rate of terraforming, let me know - I can probably come up with something that scales correctly at the extremes, even if it isn't strictly correct.
John