Amazing mnemonics, thank you for sharing. Do you practice this as a mental exercise, or do you actually need to know the day of the week for a specific date that often?
Where I have used it more often is when I am wondering "what day of the week will Christmas be this year?" or "what day of the week will my birthday fall on this year?". It's nice to be able to work those out mentally without pulling up a calendar app and tapping "next month" multiple times. But even that is a rare occurrence.