He evolved the character.
Although it does seem to me that in his two most recent, post-retirement screen appearances in the Abrams films, he hasn't really been playing Spock at all; he's just come in and been Leonard Nimoy.
I don't know how Nimoy's increasingly worse portrayal of the Spock character qualifies as "evolution." After STAR TREK II, Nimoy stopped putting any real effort into his performances. Although ...
In UNIFICATION, he seemed more interested, perhaps because he found himself playing Spock in a new situation. Might've even been due to the presence of Patrick Stewart, whose acting is world-reknown for excellent acting. In any event, Nimoy's become increasingly emaciated, over the years ... which would include his vocal chords. People say he used dentures, but I doubt he lost teeth. It seems more likely he got his teeth capped, which did not help his speech, at all. It's sobering seeing our heroes succumb to the ravages of old age.