There was no promise of a 'genesis planet', no 'Spock saves the whales'. This was the end of the movie, and as far as I knew, the end of all Trek movies. I mean, how could they do more movies if Spock wasn't in them? So Spock was dead.
I was in middle school in 1966. Spock was who I wanted to be and could never be. Spock was able to take all McCoy's insults and suspicions and racism and let them bounce off. When someone tried to beat up Spock, they got their ass handed to them. He had the answers to the questions. He wasn't the hero, but he was there, and boy was his sex life a cosmic screwup, but that wasn't till later.
So my idol was dead. Heroically, which was great, but dead. And I had to deal with that.
Then, a few years later, they came up with another movie to regrow his body and shove him back in.
I was furious. They had killed him, and then they had the GALL to say, "Ha, ha, just kidding, look, here he is!" I still have never watched STIII from one end to another. It's got some great scenes, but I can't stand it.
After 'Spock Saves the Whales', I got used to him being around again. And I could see that Leonard Nimoy was a hell of a lot better Spock than William Shatner was a Kirk.
So having Leonard Nimoy and Spock around again was kind of a freebie. He had been gone, he was back, and he was still pretty cool. Kelley and Doohan passed on, and I mourned them appropriately, but I had never wanted to be a mad genius engineer as badly as I wanted to be a Vulcan.
STL:TNG did a damn good job of giving Ambassador Spock a way to be left behind but not forgotten. I consider the two new ST movies just another crude ST timey-wimey hack, and have not seen them. The car commercial was hilarious, though.
So, here we are again, and I am not mourning Leonard Nimoy, I'm grateful for having my Yoda back for a couple more decades.