Interesting and not too complex method. Makes colors more vibrant.

3 copies of layer
top layer, desaturate w/ luminocity
invert
blur/gaussian blur (20 for 2200x1600, adjust by resolution)
reduce opacity to 35%
Merge down
Change mode of resulting merged layer to Grain merge or try others like soft light.

create dupe layer
filters / enhance / high pass
set radius to see what parts of image will be affected
when done, click okay
in mode for layer, select overlay

add 2 extra layers
invert top layer
set to grain merge
gausian blur to some number
merge down
overlay

Best explanations of masks and layers I've found so far.

Interesting way to isolate foreground of image with a lot of detail, such as strands of hair using layer mask. Need clean background to start, but interesting technique.

Old but good explainer of logic on using color averaging, then picking proper blending, which is automated currently bypasses an easy explanation of logic

Hold down control-shift-u whilst using the text box and a small letter u will appear, then type a9 and hit enter.