"it has some benefit, in the sense that it grows the economy which pays the taxes which funds things like dams and bridges and fire departments"
The inland cities won't get to see that benefit, since the train that's supposed to be providing that economic growth would only be doing so for two coastal areas.
Unless you're claiming here that the prosperity of San Francisco and Los Angeles means that Fresno and Bakersfield magically become richer, in which case that'd just be trickle-down economics (but maybe that'd be fitting for the state where Reagan was Governor).
"Frankly, I wish we'd stop using my tax dollars for road subsidies in Flyover, Oklabraska"
Okay, you're free to vote that way. I don't wish that, and I'll tend to vote accordingly. Or, more precisely: I'll be inclined to vote for politicians who in turn vote/act/etc. accordingly.
(I do agree with you about the proliferation of military assault vehicles in civilian police departments, for what it's worth; that's a waste of money that'd be better spent elsewhere, like on transportation infrastructure).
In the case of this train, the point of the State of California funding it is for the State of California as a whole to benefit. If San Francisco and Los Angeles want to build a train that only connects those two cities and leave the rest of the state high and dry, then they can spend their own money on it. If you expect us inland Californians to pitch in, then the least y'all can do is give us some stops in the bigger of our cities.
"They're already getting more than their fair share in Bakersfield"
It's called redistribution of wealth. Just like how some individuals are disadvantaged relative to others, some cities are disadvantaged relative to others. Just like how we help subsidize the welfare of less-fortunate Americans by asking for a greater contribution from more-fortunate Americans, we help subsidize the welfare of less-fortunate cities by asking for a greater contribution from more-fortunate cities.
The subsidy arrow in America points solidly toward the middle because that's where it's needed most right now. Trying to move the arrow back toward the coasts will only amplify that need.