Nick:

I don't think discovering better instrumental values toward the same terminal values you always had counts as moral progress, at least if those terminal values are consciously, explicitly held.

Why on earth not? Aristotle thought some people were naturally suited for slavery. We now know that's not true. Why isn't that moral progress?

(Similarly, general improvements in reasoning, to the extent they allow us to reject bad moral arguments as well as more testable kinds of bad arguments, could count as moral progress.)