I feel with you Richard. Especially due to recent discussion in the realism thread you may become excited trying these things.
Usually I stick pretty much to the default values and do not deviate too much from them.
For sun's strength I sometimes bring it down to 3 and sometimes up to 5, but not more.
Only one exception: sunsets. There I tend to use values of around 10 or more, especially with very low sun elevations.
What you may try indeed is disabling the surface shader chain and re-balance that lighting, then re-enable surface shaders and see if they hold up.
If you need to make the surfaces darker/brighter then you can save yourself a lot of time by feeding the entire surface shaders chain as colour input of a surface layer and use the diffuse colour setting as multiplier for diffuse colour brightness. Very handy.
Another thing I often stick too is that I always use max albedo 100% for my clouds (0.25 for colour, that is).
Then I adjust lighting in such a way that my EXR can contain the cloud's brightness easily. Say about 3/4-way of the histogram.
Even in EXR you can get over-exposed areas of atmosphere easily.
If it's about 3/4-way of the histogram you can push/pull it a bit when playing with exposure/gamma.
This all depends on your area of interest of course. Now I'm discussing mostly atmosphere, don't know why actually
The area of interest in this contest is roads and thus surfaces, so for the moment I would base these kind of decisions for your surfaces.
So in retrospect, you may not need to refine all your surfaces, but only set sun strength to default, adjust camera exposure (for vegetation mostly) and then refine atmosphere. Perhaps that's the most effective approach?
Good luck!
