Some more things that happens in real life... The way stars, planets and moons are seen through a thick atmosphere. For example, the moon appear big seen from horizo, while it appears smaller when high in sky. My suggestion is to put a code or algoritm so that worlds seen from a thick atmosphere will suffer such effect. The more pressurized the air is, the stronger will be that effect of distortion of shape. And another thing, stars seen from an atmosphere shiny, they are not static as they appear in space engine, right? Ah, yes, there's another thing... fog.
The atmosphere code should have another algoritm for fog, independent from the model of the atmosphere.
Let's take Titan for example. In space engine the surface of Titan looks crystal clean, but it's known that the air of Titan is very foggy, in a way that it's difficult to see distant things from the surface. And that may be simple to make, it seems. So instead of having that odd cloud layer, it would have a new fog layer with some few clouds of methane. Because that opaque layer is not really a cloud, but a smog or something like that. The fog doesn't have to be volumetric, only the clouds. The more near the surface, the stronger should be the fog effect, for worlds that have more opaque atmospheres.
Another effect is that related to Venus, the high temperatures distort the shape of land. An algoritm for such effect should be implemented too, for hot planets or moons, specially with dense atmospheres. The higher the value, the stronger the effect, same for the fog effect and for the distortion of shape related to the size of worlds and stars seen from the horizon.
Fata morgana effect is also an advice too, specially for hot desert planets.