Cuckoo isn't random, but it has less defined separation between the bars of white and black. Imagine the difference between drawing black lines with a marker versus with a crayon (using minimal pressure). A good photo with two quality birds side by side would really help.
BTW, I'm pretty sure that the cuckoo silkies I occasionally hatch get their barring from a barred rock, so I suppose they are barred and not cuckoo, but since the difference would not show on silkie feathers I don;t think the name difference means much here.
People don't usually pay much for birds with an undeveloped variety (notice I did not say unrecognised). as compared with birds where the quality has been worked on and improved. If you're willing to work on the generations it would take to achieve quality birds with quality plumage you could make as much as with any other variety of equal quality.
If you just want a quick buck, best to work with already perfected varieties.