Piotr Wozniak has some material on creating/designing more concrete cards for spaced repetition that I’ve found generally helpful. I know that Andy Matuschak and Soren Bjornstad have some ideas, experience, and research in the space but I’ve yet to see more deep research on the effectiveness of these more specific practices at scale or beyond the anecdotal.
Marshall, in looking at your cards, I’m curious how easy/hard you feel it is to remember longer portions of full quotes like your H.L. Menken example using only spaced repetition? I usually find it far more taxing and not as long lasting as using other more classical mnemonic methods (method of loci/songlines).