A fun challenge, Mal. Thanks for posting your pic.
At least in your interpretation one could figure out the subject of your art. In mine I may have gone too far.
Resized image to 14" wide, 80 ppi.
Layer stack (top to bottom)
* Stroke frame
* Levels adjustment layer (contrast)
* Hue/Saturation adjutment layer (color saturation)
* (Color Burn) Copy of Background
* (Darken) Detail Lines ##
* (Normal) Copy of Background + Impressionist > Conte > Unsmudged Monochrome (Color setting changed from grayscale to color).
* Background (turned off; not used)
- - - - - - -
## Layer = Detail Lines
* Duplicate Background
* Blur > Smart Blur > Normal. Radius = 25, Threshold = 90.
* Stylize > Diffuse > Anisotropic
* Sharpen > Unsharp Mask (100,45) to tighten up the lines a bit.
* Click on Channels tab
* Ctrl + click on RGB channel to "load the selection" (marching ants)
* Click on Layers tab
* Click on (highlight) BG layer
* Ctrl + J to create a new layer based on the active selection
* Drag new layer above the Impressionist layer
* Change blend mode to Darken
* Add layer mask
* Airbrush black to erase unwanted lines or tone down too dark lines
Why bother? This method renders lines that are based on colors in the original image, so they are not completely black. Smart Blur > Edge Only renders white lines on black, that when inverted, yields all black lines.
~Danny~