Small world, I was there also! As I recall, the Grateful Dead were at the eastern side of the music concourse in GG Park. I was within 20 feet of them. I brought their LP album and had all the band members sign the cover. I was very upset when I found out my sister gave the album away to a friend. It would be worth thousands today.
You're right, about how many young people came after that song. Haight Street and the park panhandle were easy going with free band concerts (Jefferson Airship etc.), and all that changed to crowded conditions in 1968 (and the bands doing paid concerts). So many people came to SF that were from outside California.
Those were the days. Young and reckless as hell.