I think prog burnt out around 74/75, after 5 years of incredible development and music the big bands started to run out of ideas. For me ELP lost it after Brain Salad Surgery (Love Beach was enough to make me puke), Yes after Relayer, Genesis when Hacket left. King Crimson kept the flame alight but having said that I found some of their albums impenetrable.
My preferences moved to folk and folk rock, Bands like Planxty, Ossian, The Battle Field Band, Five hand Reel, Richard and Linda Thompson but I never lost the love of classic prog rock.
These days? Yes have released "Fly from Here" their best album since Relayer, unfortunately without the ailing Jon Anderson. I have recently got into Syzygy, Touchstone, The Reasoning, Panic Room and Mostly Autumn. But is this is this music progressive or regressive? But I am playing Greenslade, The Strawbs, Yes, Colosseum, King Crimson, The Nice to name a few again on a regular basis.