I would have thought it would be more important for older spock to let younger Spock know about the Hobus Star incident - this event is outwith any influence of nero's timeline changes and is guarunteed to occur in both universes.
The problem is that Red Matter was deemed to be the only solution to the Hobus Star exploding and was created by the Vulcan Science Academy at some point in the future after the events of the movie - except it won't anymore as Vulcan was destroyed. Thus this new universe will end in the late 24th century unless someone deals with the Hobus Star.