I think the current lighting looks great, and I think harder, higher-contrast lighting would look great as well... just an idea, but I think what's possibly wrong at the moment is that everything looks exactly the same, regardless of how much light there is, i.e. how far from the nearest star.
So lets say you're flying through Saturn's rings, 10AU from the Sun so it's about as bright as a cloudy day on Earth. I think the current lighting is spot-on for this.
Now say you're in Earth orbit, sunlight is 100x brighter. We've all seen the pictures / videos from the ISS, everything looks bright and contrasty.
If we move in again to Mercury, 10x brighter again, and it'd be great to get a real impression of the intensity and harshness of the environment. Lots of max brightness and glare for anything exposed to the sun, and shadows would be almost completely black in comparison.
So I guess what I'm suggesting would be to vary the contrast to reflect the intensity of the light, at the moment it's a bit like the ambient light scales up with the brightness of the sunlight.
