So here's the final polish -- but not as final as I thought. Looking at this, I just noticed that the two dark patches in the middle of the back slope are obtrusive. I found myself removing just about every little speckle of ink -- I've never used the rubber stamp tool this extensively before.
And here I've gone through and messed with adjustment layers -- Levels and Brightness and Contrast -- to enhance the sense of depth before I get into color. I wasn't that fond of this piece until now but this subtle revision really brings it together for me.