I believe that one of the problems with the Toscana event in particular has to do with a combination of how the light cones are rendered, low reflection rendering indices, and a low dynamic lighting range.
1) Light cones as rendered (and also as in real life headlights) have a constant pitch value; the headlights in the game aren't illuminating *UP* the face of the hill, they point straight into the hill. Understandably, this becomes an issue on hillier circuits, and the generated Toscana track for the event has some of the most dramatic elevation changes of any track in the game. This alone is not a problem - it is realistic behavior for real-world headlights. However...
2) ...all light reflects from surfaces, including roads. Projected light, such as that thrown from a car's headlights a) diffuses on a rough surface and b) reflects back from that surface. It is debatable, but in my opinion, the lighting engine in the game does not do an adequate job of spreading light that is reflecting off of the ground, and therefore lighting up more of the (very) immediate surroundings.
3) Lastly, displayable dynamic range plays a large part in how a scene is perceived. A low dynamic range 'squashes' the amount of light in the scene, which is the difference between professional and amateur photography and videography. Gran Turismo does not have a very high dynamic range, and therefore bright lights and skies look 'blown out' and there is not enough detail in dark areas.