Yet in "into darkness" he pops up for 30 seconds in one of the most forced Cameos in cinematic history.
I disagree. His cameo was essential to nuSpock's next actions. I enjoyed seeing him again and will as long as he will appear.
The difference was that in GEN he wasn't going to be important to the script. He was going to just be there to be sad when Kirk died. That ignores the chance that Spock will be 'around' 80 years later, that he's smart and would probably have researched the Nexus like Soran did and realised that Kirk might still be alive and would have been interested in finding him.
I saw Shatner and Nimoy in Vegas 2009. Nimoy explained in a sort of comedy routine with Shatner that if he Nimoy had appeared in GEN that Kirk would never have died. Shatner pretends to doubt him but Nimoy eventually 'convinces' him. He tells Shatner he should have never appeared in the movie. If you believe Nimoy here, and I have no reason not to, he thought that Kirk shouldn't have died and not so badly (and he's not Robinson Crusoe there)