SpaceX is not revolutionary, it is evolutionary, as rocket's discipline was already well known when they started. You know who was revolutionary with rockets?
This man: https://en.wikipedia.org/wiki/Wernher_von_Braun
As a child, he was playing with friends launching rockets(and burning crop fields when they failed), actually as a hobby. I call hobby studding something freely just for the sake of it.
Hoover dam is a terrible example, because almost 100 people died building it, and it should not be necessary killing people for building things like a dam, it is actually much better building things without casualties, the project runs smoothier and faster. And it is a known discipline that Romans already did 2000 years ago.
Cinema, in the words of the Lumiere brothers was just a hobby with no real monetary value.
Most of Newton time was studying freely esotericism and alchemy. Most of it gave nothing to the world, like philosophy, it was done for the sake of it(science and all sciences come from it, so a very small portion of it paid off).
Mr Boole spent enormous amount of time trying to prove the existence of God, and invented Boole algebra as a result. It was of no practical use until more than one century later.
The neuron was discovered because of the photography hobby of Ramón y Cajal, staining cells so you can see it.
Most of the greatest discoveries in things like Mathematics were done by outsiders, like lawyers that were only interested on a very narrow part of it. And it was a hobby.