Obviously certain threats like the Borg or V'ger are constants and Spock would be remiss in keeping silent.
Other threats are more vague and may or may not take place in a shifting timeline.
The Klingons... Praxis is still on course to explode. What does Spock do? If the Klingons somehow become allies then telling them that Praxis is prepped to go boom would be a point of honor. If they are still adversaries, does Spock warn them and try to earn their goodwill? This might fall short of the original historical agreements. Or would the Klingons even listen? Or does he keep silent and the Empire might figure out he knew and consider his silence dishonorable and treacherous?
Technical developments. While he wants the Federation prepared, I think it would be too dangerous to giveaway too much tech. It would be easy for the Federation's neighbors to become alarmed if the Feds suddenly leap ahead in tech. This would be dangerous. Also it would affect companies and many other things. Then again, taking a guiding hand on some individuals. (Like Richard Daystrom) might not be a bad idea. Certainly do not expect the M-5 Wargames disaster to repeat.
Spock is in a very grey area... But then Command is all about those grey areas and in that, Spock has seen the best in action.
Ever notice that many of the same people who want variety in life frown very hard on vanilla... But without Vanilla, Baskin Robbins just wouldn't BE 31 flavors.