It's already been demonstrated that there is different and newer technology as a result of the divergence back when Nero arrived, and before Spock did.
My opinion is that if I were Spock I would be very careful about interfering dramatically in any significant way. The timeline has already been altered, fair enough, but that's no particular reason to further that any more than has been done.
There was a thread a while back and I recall a lot of people felt that he should reveal as much as he wanted to however, and I can see why, because the same argument applies. The timeline is changed already.
Khan might also be found sooner, not later.
But the bottom line is that I think he should keep his knowledge to himself unless the situation is severe enough to warrant breaking his silence.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist