Outside of population growth or worker shenanigans, Aurora appears to strongly incentivise having a single large colony over multiple smaller colonies, both to take advantage of strong leader bonuses and to minimise micro. Smaller colonies only really make sense to boost population growth or to act as forward bases, since having a large number of small industrial centres makes any ind of industrial growth an utter pain. Even with regards to resources, it's often best to dump all your mining complexes on that one world with ridiculous deposits at outrageous accessibilities.
As a way to make smaller colonies more viable (so we can all get a slice of that nice, thematic SPACE RACE!), I'd like to suggest that mineral accessibility on system bodies scale with the number of mines present on them, with a larger number of mines giving diminishing results on smaller bodies.
You might be able to accommodate, say, 1,000 mines on Earth without running into diminishing returns, but 10,000 mines may produce only twice as many minerals, so it would be better to spread this across ten Earth-sized bodies. For a system body with a smaller surface area, the limit might be hit much, much sooner. I'd anticipate that to balance this, accesibilities in general might need to be revised upwards.