On AC, if the fares are materially lower, than I will go for it. I have found food tastes better and seats have become more comfortable if I can save a lot of money
The money saved will be used for other things on my trip. I have found AC catering better (personal opinion), and services are more consistent. However, customer support and services are the weakest links of AC.

Perhaps It is just me since I am a lifetime GS, for personal travel out of my own pocket, I go for upgrades using PPs as first option, if I reasonably assess my upgrade opportunity is low, then my second option is looking for the cheapest business fares on fellow *A carriers, and then shop around other airlines for the best fare.