Glad to know I'm not the only one that finds the Calculations dialog a little daunting! (LOL)
Working from bottom layer to top...
Duplicate original Background. Name it "A."
A: Virtual Painter - Impasto
A: Distort > Ocean Ripple (5,5)
A: Edit > Fade (to about 50%; throttle back the Ocean Ripple effect, but disguise the VP effect a bit)
B (next to top layer): Duplicate Background and drag to the top of the layer stack. Name it "B."
B: Impressionist: Crayon > Short Choppy Strokes
B: Impressionist: Charcoal > Default (this chopped that patch of blue sky)
B: Layer > Add Layer Mask > Hide All
B: Set foregrond color to white, selected Brush tool from the Tools palette, selected a Chalk brush from the brushes palette, set opacity to ~ 50%, flow ~ 50%. Painted white on Layer mask in sky area to reveal the 'arty-looking' sky in layer C.
C: (Top layer): Added a Hue/Sat adjustment layer. Saturation = +25 to rev up the colors a bit.