The problem is that the tension in the trailer cable will pull back any magnetic repulsion you get.
A fossil fuel propulsion system may be 'heavy' in terms of the fuel, but the engine itself is relatively straightforward and light. Compare that with a magnetic/ion/nuclear propulsion system where the reactor, shielding, coils, magnets, etc. will weigh a lot.
Oxygen is an oxidiser
. Not a fuel.
Space may be a near vacuum but who said you can't mine stuff along the way? [;)]
Commerce (and maybe a good marketing team) can turn 'not bright ideas' into good ones. Hey, a good insurance salesman can con you bankrupt and keep you smiling along the way [s(]
The levitation so far accomplished has only been miniscule. Don't forget magnets are big, heavy blocks of ferritic material. If you're talking about ceramic-based superconductors, then you will still need a power plant and a cryogenic cooling system (at least until room temp. superconductors are developed).