As much as I love Spock, old or new, I felt it wasn't needed. Much like making Harrison Khan, Spock gave this new era of Trek an old guard blessing, his return felt strictly to be fan service. Which is fine, but personally I would have left it out. Literally, nothing in the exchange, or what is implied in the exchange, is paid off later. NuSpock could just have easily come up with the idea to trick Khan, and it would have played very nicely into the role reversal theme already present in the film.