So in a Timeline where no war breaks out with America, and Mexico, and it keeps all its territories, what would happen to the Gold Rush? Would it be butterflied, would it still happen, if it does, do tons of Mexicans flock over there? And if it does happen, how much money would Mexico get from it, and what would be the consequences?
Well, one way this could happen would be that the Cherokees end up in Texas instead of white settlers which would keep the US from buying Texas. I am guessing maybe Mexico can still sell some land to the US if need be (up to the Rocky Mountains), but that is optional.
Mexican settlers discovering gold would be a massive boon for the nation. It would incentivize alot of people to settle the north and have Mexico better integrate the northern territories into the whole. Whether or not they will do better with the natives is up to the policy, but I think they would probably fare better. A Mexico-based California would lead to the rest of the North being more populated and might invite some people to Mexico (though I picture it would be non-whites like the Chinese to do so).
The US would probably end up pissed but I doubt they could get away with declaring war over it.
The money would help, but it would all depend where it would go. It would depend on who was president. If Mariano Arista was president, he could use the gold to help bring fiscal responsability to the nation if he could overcome the plague of conservative general staff he had (though the govenrment would be more stable with no Mexican-American war and so I don't know who could've been president by this point.)
As for other consequences, a bigger Mexico would change the American Civil War by a fair bit. Mexico would probably remain neutral, albeit supporting the Union, especially if the CSA still wanted to try and take land from Mexico if they won.