I never get upgraded on my weekly DTW-LAX roundtrip trek but I think it has still been worth it...free Economy Comfort as long as I book a decent amount in advance and it isn't all taken already, free food item / drink as long as I print my ticket at home, and a ton of miles of which I've used roughly 100,000 on three separate trips that saved me from spending about $1500.
I flew American for a bit because they had a better schedule for a few months and honestly their planes suck, I faced delays seemingly every week, and the redemption of miles is less valuable out of a Delta hub like DTW.
It sucks not getting upgraded ever I guess but it's become more of a treat when it does happen. And all I really want is a comfortable ride without delays and I've gotten that fairly consistently.