

It would work if the repulsion/attraction only went in 1 direction. But since it goes both ways, they just cancel out.
Conversely, the fan version of this idea (fan blowing into a sail) does actually work. But it’s nowhere near as efficient as simply turning the fan away from the sail to push you the normal way.
No, because the force of attraction is still working in both directions just not as strongly as it would with two magnets.