I was underwhelmed with DeYoung as well. The "Summer of Love" wasn't a summer and it was not restricted to pot, music or love. Music and posters were the entertainment, not the core of what was happening. That summer was a confluence of lot of breakout ideas (many contradictory of each other): the war and the movement against it was huge. Eastern mysticism, Jesus freaks, back to the land folks, weed worship, organic food, new art forms, poetry, brown rice, the Whole Earth Catalog, community organizing, civil rights, gay rights, women's lib . . . So much stuff I can't remember it all!
The '60s blew the lid off ideas that had been percolating for years and the city provided a venue for them to all emerge. Great as the music and posters were, they were almost incidental to the real show: whole new paradigms of thinking, governing, and living emerging from their cocoons.