IMO, whether or not you can get away with CCD and QD for light dirt depends a lot on both the color of the car, and how scratch-resistant the paint is. There's probably no definitive answer.
I'm fortunate; I've used Spray & Wipe on my silver WRX for some unpleasant winter road films that I'm sure would make Autopian purists cringe, but the finish still looks good overall. Yes, I can see fine scratches in the clear, but because the silver on '02 WRXes is so damn bright, I'm the only one that really knows that they are there (and I can only see them in certain light). The scratches are fine enough that they don't detract from the silver "pop", and they polish out easily when I do my twice-annual full detail. For me, the convenience of using the CCD and QD for minor dirt outweighs the minor marring that I introduce on the finish. OTOH, with a different color or more scratch-prone paint, I might have torched my CCD long ago . . .
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