"Nicer" is completely subjective and relative. If she has a new Mercedes S Class and he has a new Mercedes C Class, they're both nice cars, but I guess some would say that hers is nicer than his. :dunno: But if she has a clean later model Toyota Camry and he has an '89 IROC-Z Camaro that's got a dent in one fender, the other fender is rusted out, the seats are ripped to shreds and the inside smells like he's been carrying around a dead hooker in the trunk for six months... well, no, that relationship might not work out.
But it all depends. Some people are into cars and some are not. Some people are into material things and some are not. But whether a girl is into cars and material things or not, if a guy has a car, I'd say the average girl would be much more impressed by a guy who has a decent looking, clean, well maintained ride than a hunk of junk that looks like it's on its last legs. If you can't even keep your car clean, that might suggest something about you that would turn a girl off.