We're running fast out of helium down here at earth and it's very useful for superconductors, perhaps it can become economically viable to do helium mining on the moon in some far future (except, in the far future we'll probably have unlimited amounts of free helium from our fusion power plants) ... but using helium as a fuel, that I don't understand at all, care to elaborate on that part?

The only thing I can think of is to use it as propellant mass in an ion engine. A quick google search gave me this one: https://www.quora.com/Can-we-use-helium-for-ion-thruster - it should be possible to use helium, but it's rather sub-optimal.