In the world of horribly redundant superhero vehicles, the Supermobile reigns supreme!
And I suppose, among the vast science and technological resources that Superman would have at his disposal, a super vehicle of some kind makes sense.
My favorite aspect of the Supermobile is the Super-visor, a binocular like apparatus that rises from the dashboard, with a dial allowing Superman the option of x-ray, telescopic, infrared, and normal vision. Normal vision? Why is there a setting for normal vision? If he wanted normal vision, all he'd have to do is move his head to the side three inches.
I could see the Supermobile being useful to Superman as a FTL ship for travelling between starsystems, with a computer linked to the Forteress of Solitude's own, and with sensors, weapons and equipment that could be useful to Superman on a number of missions on far-off worlds.
Of course, the advantage to having Superman's powers would be the economy in terms of life-support needs..