Len, thanks for your latest. I'll get back with some more comments after I've thought about it all a bit. I'll state the obvious, of course, that post editing doesn't address limitations to control over rendering.

Aldaron, thanks for explaining shadows vis a vis the darkened room - that's exactly right. It is an extreme example but it does illustrate the point.

The room I'm in now is fairly well lit (artificially) but there are many areas of apparent blackness, mostly under objects that stand just off a surface. Yes, I know that some photons are making their way into those dim areas, but if we're talking about realistic renders then we should be attempting to reproduce what we see.

It's interesting to look at the search results for "sunny day" on Google images. Most pictures of brightly lit sunny scenes have a lot of areas of blackness, and it's surprising just how dark some shadows are even out in the open under blue skies. The human eye/brain combination can perceive a much higher range of contrast than photographic film and chip, but even so there's a lot of darkness when the sun is out (especially in my town ;-)).

That was why I started this shadows=x ball rolling. With shadows as low as 50 there'll never be appropriately dark areas in renders that aspire to realism. I guess Len agrees to some extent, otherwise he wouldn't have bothered with the latest exploration (Pro-Render 0.9713 ;-)).