Yes, I do realise he had many projects on his plate at the time of Generations. What I was trying to say is that now that he is older maybe his attitude toward only taking a role that is essential to the plot has mellowed.
Or maybe it's no longer a consideration at all anymore. After all, Nimoy is technically retired. In the past dozen years, he hasn't done any on-camera acting except
in Bad Robot productions, and in that car commercial he did with Quinto. So he's not making choices based on what suits his career, because he's no longer pursuing a career. He's retired, and that means he does things because he thinks they'll be fun, because he gets to spend time with people he likes.