FreeGameDev

shadows in cloudy or rainy tracks don't look so realistic for me

for example F8-blurX3

sharp shadows from trees look like the sun is shining

do you think this is important or not?

Hmm. You mean that the shadow should be very blured, or just some blob or much less visible.
Yeah that's either not possible at all or very difficult. Ugh, yeah shadows in SR were always buggy.
To make it less visible we could adjust ambient (more) and diffuse (less), but heh, I fear that something could go wrong (not follow this, like water) IDK.

normally when you have clouds somewhere and the sun is behind these clouds, you don't have shadows (an option to disable shadows for a track could solve this)

Right true. But yeah this would look a bit ugly with no shadows at all. And other aren't possible.