I've been bugged by the smol station sprites as well. Astropoli are HUGE in comparison on the map, but practically they reach the same size/population. I think it would be safe to simply replace the mining station sprite with the astropolis one. The difference is purely aesthetic though. Perhaps a skilled artist could contribute original and separate sprites for ore and gas stations, as well as astropoli...
Somewhat related: I've noticed a pretty significant issue when turning on the "Cramped Quarters" effect. Though I personally think it should be on by default, as building space stations should be more money and time-consuming than colonizing a planet, when you also turn on the setting for non-player factions (which also makes sense), they all immediately gain negative growth when above size 3.
I'm not saying that the factions should build station expansions the same way the player does; but maybe hardcode the "Cramped Quarters" setting to be at a certain level of already built expansions to counteract the negative growth for other factions' stations?