This is great work and presenting those options really helps!
However, It’s a little bit hard to tell via this link as you zoned the screenshot and not take a full screen. (At least, I have harder time to realize the entire desktop with it ;)).
I would be, though, in favor of: box-shadow 1px, 2px blur, spread 1 or 2px (don’t need to be too noticeable).
For the Dark panel version, I really think it should be solid, without opacity, and so I like your proposal of
box-shadow: 0 1px 2px 2px rgba(0, 0, 0, 0.3) here.
What do other people think?