It really depends on the car. It has to look classy and not out of place. Like for an example a woodgrain interior on an old Honda Civic is so out of place. On the new Fiat 500 a woodgrain interior will look so good and add to the timeless classy look of the Fiat 500.
carbon fiber would only look good on sporty cars. unfortunately the 500 isnt really that. some of its special editions do offer sport car performance but looks wise it still looks like a modern retake on a classic.
I think the original concept of this car was more humble than what it has become. You could customize, or just wait a year or two for Fiat to improve it. It looks nice, but it may not really be as nice as it looks in pictures.
But then I think it will become more pricey, similar to what happened with the mini cooper. They priced it quite low at introduction, but then the law of supply and demand kicked in and drove up the price.