For US-HKG TPAC, the fare difference from AA codeshares is typically about US$600 (US$1900 vs US$1300), and less than the copay part of the miles+copay for upgrading on AA. I find it well worth it; the much lower ($100, previously $50) change fee is also very helpful.

The non-codeshare AA-earning H-fares are up around $1700 a lot lately, so that's a truly trivial difference given the difference in comfort.

If I were flying the cheapest non-mile-earning fares, I'd probably feel differently as those are around $900 and so Premium Economy would be more than doubled.