Yes, my mom loved the original series and so we used to watch it in reruns when I was a kid.
I think conventions started in like 72-73, but in 75-76 we went to something that was ... a version of it?
It filled the 14k Hartford Civic Center and featured Roddenberry, Shatner, Nimoy and others speaking and showing clips and bloopers from the original show.
I'm sure these was more too it. But 10 year old me, I mostly remember the cool green glow sticks everyone had that lit up the arena when the lights went down. ;