I also saw it first run on NBC. I was 8 and it was the show I most looked forward to. "One of Our Planets is Missing" is the episode I remember most vividly from that period, probably because I audio taped it. Back then, Saturday morning TV was a wonderland for kids and it depresses me to talk to younger people who have no idea what I mean by "Saturday Morning cartoons."
"You can watch cartoons anytime with Cartoon Network."
This was back when cartoon versions of popular show was all the rage, and a few of them utilized the original actors, such as The Brady Kids, the New Adventures of Gilligan, Emergency Plus 4, etc. 60's TV shows were being revivied in animation pretty often then. When TAS was cancelled, I only learned about it when I tuned in one morning to be greeted by "Star Trek will no longer be seen. Now stay tuned for Westwind!" Needless to say, I never watched "Westwind."
When Nick began running it in the 80's, I was thrilled. I videotaped a couple, but I only had like 4 blanks and they were expensive! I got the whole run thru a special offer from Columbia House. They were calling subscribers of the original series tapes and offering the whole animated series and a "Star Trek Enterprise mobile" made of cardboard. My sister let me charge it on her card. :-)
Later on I got the laserdiscs and then the DVDs. Great stuff and fond memories.