The first time I ever heard GG, I walked into a room where someone had Free Hand on the phonograph. I was instantaneously converted. I saw several shows in the NYC area between 1975 and, sometime after 1975. There was the Academy of Music (or was it the Palladium by then?) - a concert that left me truly speechless, Central Park, the night Starcastle opened for them, and Avery Fisher Hall - not long after its complete renovation in order to improve acoustics, a real treat.
After one of the shows, a friend and I did a count of all of the instruments we had seen played by GG that evening. We came up with 27.
In those days, being a fan of GG (as well as Zappa, Genesis, Yes, Tull, ELP), one truly felt like a member of a bizarre cult. We sure all looked the part. One thing I remember which illustrated this sense of community was that the pre-show music at the GG concert at Avery Fisher Hall was Zappa (either Roxy & Elsewhere or Overnite Sensation), and, around the same time, the pre-show music for a Zappa concert (probably at the Palladium) was GG (Free Hand I think). Probably just some sound engineers' idea of fun, but it seemed right.