Agree on the split and I have arrived at a stricter version: nothing about me, only about the work.
Anything biographical produces a tone shift that feels like rapport and is not information. It made answers longer and slightly matey and never more correct. Removing all of it made the output blunter and better.
The anti-preferences point I would extend, because it is underrated. The highest-value entries are all negative, do not do X, for the reason you gave: they fight a default. A positive preference is usually something I would have specified in the prompt anyway when it mattered. A negative one is something I would have to remember to specify every single time, and would not.
If someone is starting from scratch I would tell them to store nothing but a list of things not to do, for a month, and see how much of the rest they miss. In my case: almost none of it.