better buy some farmland then gold. Gold doesn't produce anything when you buy it; It just sits there. Farmland if you work on it it produces something. You can sell i tand repeat.
we are talking about solar system exploration without needing to spend propellant to make it go (once it's in orbit). That changes things dramatically. Right now virtually all space travel (with the exception of some preliminary solar sail tests) is done on the principle of shooting particles out the back of the spacecraft at high speeds, whether propelled by chemical reaction (low efficiency high thrust) or electromagnetically accelerated ionized gas (high efficiency low thrust). That means you have to spend fuel to accelerate the fuel you're carrying with you. This creates a nasty feedback loop. This thruster would change all that since it doesn't use propellant, it just needs electricity which it can get "for free" from the sun. The low thrust of the first generation design means it will only be useful once you're in orbit, but once there you can slowly accelerate persistently.
According to some tests and predictions this should produce more thrust than an ion engine, but still far less than a chemical rocket. That's ok though because you can leave it on for as long as you have power and as long as the device will work (expected lifetime around 15 years I think according to the inventor?). NASA's version produced about as much thrust as a typical ion engine. A second generation design being proposed by the inventor is said to be capable of producing even more acceleration, around half a meter per second^2, so it could supplement air travel and even assist payloads in getting to space, but it would require liquid cryogenics (which would eventually be consumed). It still remains to be proven, but at least the initial NASA test yielded surprisingly positive results. We'll see.