You asked what advantage would it have over rolling rubber, not how would one do it (you wouldn't with current understanding of physics and energy density/portability). Any at advantage vehicle like that is still in the realm of scifi.
Yes but it collides with our understanding of physics as well. Floating anything with significant weight within an air atmosphere requires constant power, you will at least have to profuce an upwards force that is equivalent to the downwards force. Depending on how efficiently that force is transfered you may need much more. A wheel made of rubber or steel (trains are freakingly efficient!) does give you that much cheaper.
Now theoretically one could envision some energy form that is so abundant it doesn't matter anymore that you constantly fight gravity, sure. But what most people seem to imagine is some magical tech that decouples the vehicle from the force of gravity, while still coupling it to the planet (or whatever the next relevant relevant frame of reference is) somehow. This kind of magical tech makes sense in films or scifi books, but if we just collect together what it would need to be, it is hard to envision any actual potential mechanism short of "we live in a Matrix and we lesrn to control the program".
That's a good question. When (if) we figure out how to practically travel at FTL speeds with a "warp drive", we might figure out the answer to this question too.
To be honest I think FTL is likelier than magical "sticks you to a fixed point in space relative to a rotating planet"-technology.
Sure you can do that with pushing air and a global positioning system, so if eventually we invent an eventual anti-gravity drive or something that may be used for the same thing. But wether such an entirely fictional device could be then made to (1) fit into a car sized vehicle and (2) be powered by whatever the most powerful mobile energy source is at that time and (3) become affordable to anyone outside of the 0.01% is another question.
>To be honest I think FTL is likelier than magical "sticks you to a fixed point in space relative to a rotating planet"-technology.
I disagree. I'm no physicist, but given how gravity seems to be related to the structure of spacetime according to Einsteinian physics, and a lot of FTL ideas seem to center on the idea of "warping" spacetime, I suspect the two are highly related, and if FTL is possible at all, it'll be also related to artificial gravity.