Not sure if we are going for data points, but thought I'd share my experience:
I have a cheap work trip to BKK this week (Economy S class ticket). CX is looking for a minimum of 2000HKD + 70HKD taxes per leg for an upgrade, which seems excessive considering that you can likely buy a return for less than the combined 6000HKD that would cost me for the two flights. I won't be upgrading.

This flight would have me tagged as an BA Emerald so they should know I don't really need the lounge.

However, I was interested to notice that even though the flight includes other airline legs (I fly on to Laos with TG a few days later) it still seemed to work.