Do dream cards show up more often with a higher Nightmares quality?
Ok, but even though these cards are meant to be nightmares of a sort, I can still get them just as often with low, or no nightmares quality?
Yes. The rate at which the productive Recurring Dreams-cards (i. e. those that increase your Having Recurring Dreams quality by an appreciable amount, and not just Nightmares) show up depends entirely on the fickle moods of the Random Number Goddess.
Although now that you mention it, that would be an interesting mechanic…