But what else changes in the process? That is the thing you can never determine until you've committed to interfering with an event that has already unfolded.
Indeed, everything Old Spock does with what he knows will undoubtedly cause a Borg incursion resulting in the end of the universe. Everything Nu Spock does, however, will turn out well when he acts on what he knows (which is much less).
What you fundamentally don't get is that Spock is not from their
future. Spock came from a different timeline. There is no future here for Spock to destroy. Their future, at this point, does not exist yet. He is not changing anything that "already exists."
What will happen in this universe cannot be determined until agents in his timeline (the nu timeline) decide what to do in response to the information they have. Spock is one of the agents in this nexus of decision. If Spock decides NOT to help this will have an impact on the future. If Spock DOES help, this will shape the future. Spock cannot "NOT influence the future" now, because he is a part of this timeline.
It's not a question of whether he does participate, but how
he participates in this timeline.
Take your drowning child in the swimming pool. Spur of the moment, I would rush in and save him without a second thought. But five years later? I remember Timmy having a bitching pool where he ended up drowning. So I decide to go back and save him so my younger self can keep using that sweet ass pool.
But, Timmy's parents decided to have another child after Timmy's death. Without Timmy's death that child would have likely never existed. So I saved one person but I sentenced another to non-existence.
This is butterfly wings nonsense. Not nonsense in that events have have unpredictable consequences, but nonsense in that we should allegedly suppose every positive act to assist the future should be presupposed to engender the worst consequences imaginable.
This is hopelessly flawed, because NOT acting could also doom the universe!
Suppose you knew that a building had a bomb planted in it that was set to go off on a slow timer (6 months or 6 years). Would you warn the authorities or would you stand mute?
Your analysis on the proximity of the impact is exactly backwards. The more time you have to intervene and the more certainty you have of outcome (Spock has one the best epistemic vantage points in his universe), the greater responsibility you have to act.