That's one of the reasons the hoover dam was made: to have a big project that would get money going around again.

Its for this reason that it's pointless to cut nasa spending because it costs money. The money is going back into the economy. It didn't magically get lost.
As long as it is going around, it has a positive effect.

For the same reason it would be better to allow easy legal immigration. That way, people settle and they spend their money locally. And they pay taxes. As long as the money goes around, immigrants don't 'steal' jobs, because their spending will pay for more jobs and increase the GNP.
It's only when money leaves the country that there is a problem.