This is very helpful. The only thing I would clarify is that the lesson I need to learn is that importance ≠ objectivity. (I'm not at all concerned about universality.)

I understand that you can't imagine a value being important without it being completely objective [...]. But you can start by admitting that the concept of important-to-you value is at least distinct from the concept of an objective or universal value!

I'm not sure. With a squirrel in the universe, I would have thought the universe was better with more nuts than with less. I can understand there being no objective value, but I can't understand objective value being causally or meaningfully distinct from the subjective value.

Next, imagine that there is something you care about, deeply, that just isn't an objective value, but which your world would be awful/bland/horrifying without. Now give yourself permission to care about that thing anyway.

Hm. I have no problem with 'permission'. I just find that I don't care about caring about it. If it's not actually horrible, then let the universe fill up with it! My impression is that intellectually (not viscerally, of course) I fail to weight my subjective view of things. If some mathematical proof really convinced me that something I thought subjectively horrible was objectively good, I think I would start liking it.

(The only issue, that I mentioned before, is that a sense of moral responsibility would prevent me from being convinced by a mathematical proof to suddenly acquire beliefs that would cause me to do something I've already learned is immoral. I would have to consider the probability that I'm insane or hallucinating the proof, etc.)