It's not about some analogy about breaking windows. People with government jobs do real, meaningful work. But even if they didn't, you are completely ignoring the economic impacts of what happens when all those people are laid off.
And I don't know the particulars about the rail in CA you are taking about, but I bet there were a lot of people like you saying the interstate system was going to be a wasteful spending project no one would ever use only to have it become vital arteries of our society. You say revenue projects are fairly useless but claim to know the value of high speed rail is nil?
California High Speed Rail summary.
http://en.wikipedia....High-Speed_Rail Current estimate is actually $70 billion, but that will go up. That there was success with the interstate highway system does not mean that any other government funded system in the future makes sense. You know this of course.
A high speed rail ticket from New York to Boston is about $150 per person each way, or $600 round trip for two people. And that's with most of the infrastructure that was already in place, as opposed to California where they're basically starting from scratch. I do the NY to Boston trip once every few months to visit my in-laws, and I always try to drive whenever I can, just to save money. It's different than calculating tax revenue streams considering that it depends on the health of the economy, which no one can predict. I can show you the operating deficits for the Amtrak Northeast Corridor, which has more ridership than even California is predicting for its high speed rail.
At bottom though, unless you believe in the mantra that deficits and public debt don't matter, government spending does not create prosperity, although it can be helpful to ease the pain of the business cycle. If that were the case, Detroit should be a thriving city. It isn't because it doesn't have a sustainable tax base left. If the Occupy Wall Street crowd had their way and we got rid of the investment bankers, New York City would have a lot less money to spend.
And whether those government workers are "needed" is a question that can't really be answered. It's that we should not put people on the public payroll just to give people something to do. If that lead to prosperity, then we might as well have a command economy where everyone works for the government.

I collect spores, molds and fungus.
Hello fellow American. This you should vote me. I leave power. Good. Thank you, thank you. If you vote me, I'm hot. What? Taxes, they'll be lower... son. The Democratic vote is the right thing to do Philadelphia, so do.
How do you spot risk? How do you avoid risk? And what makes it so risky?