JJeffrey, searching ExpertFlyer segment by segment shows NO C seats available flying from PHL to ZUR on AA (Flight 788) except on 10/24, 1/2/23, (checked with +- 3 days every Wednesday from now till 2/22/23). How far in advance do C upgrades show up? Looks like there are not a LOT of these for our legs.
Also checked BCN to PHL, this has more availability. 9/7, 9/8, 9/13, 10/19 (then ExpertFlyer just drop search after end of Oct 2022).
So on this strategy, I need to set alert for my segments and upgrade right away when avaialble. Do I need to have ALL segements upgradable to do? Outbound city is DEN - PHL - ZUR and then return is BCN - PHL - DEN.

Regarding Kacee comment, I agree with you as flights/logistics are changing all the time and bookign direct with airline gives most flexibility. With the LIMITED upgradability via AA, may not get upgraded. Also when chatting with Amextravel, they said the insider flights that show economy are economy plus. Do not beleive till I book and get seat selection. But this might be my best route as upgrading to business is SLIM PICKINGS!