After Levels and Hue/Saturation tweaks, basically three layers (top to bottom), all duplicates of the tuned up background.
1. Photoshop Dry Brush (for foreground detail)
2. Impressionist Conte: Contrasty rough (smaller, looser strokes)
3. Impressionist Unsmudged Monochrome, with Color > Strokes setting changed from Grayscale to Image. (broader, fuller strokes). Used for background areas.
Layer 3 created first followed by layer 2, to which a hide all layer mask was added (Layer > Add Layer Mask > Hide All). The more detailed strokes of this layer were revealed by selecting a chalk brush and airbrushing white in the foreground area on the layer mask.
Finally layer 1 was created and another hide all layer mask applied and foreground details (rider faces, bikes, etc.) added via layer mask.
After posting on the forum it occurred to me the colors were a little blah, so I added a Hue/Sat adjustment layer to the top of the layer stack and set Saturation to 50. Now,
"Those are some bright colors!"
~Danny~