The X PRIZE Foundation news list presents an article by the Wall Street Journal Online that advocates an automotive prize:
To further this effort, I'd like to see someone step up and offer a prize to the team responsible for designing and building the best new car in the world. Whoever funds the prize could define the parameters and time frame, but surely qualities would include environmental sustainability, performance, style, practicality and affordability.
The article mentions the Automotive X PRIZE, which does emphasize all of these characteristics. However, the emphasis of that prize is on the 100mpg equivalent threshold and winning a race; as I understand the prize the other characteristics just have to be good enough to make the vehicle a viable mainstream product rather than a concept car. The prize suggested by the WSJ sounds similar, but with a different balance in the required vehicle qualities.
I have to say that I'm a bit skeptical about the WSJ prize goals - you would think that companies would already, because of market forces, be trying to offer the "best new car in the world" when all factors are taken into account. Focusing on 100mpge as the Automotive X PRIZE does allows a particular problem to be addressed that perhaps isn't getting enough attention because market forces don't emphasize political or environmental downsides of low mileage cars. If it were me designing the prize I might make a "2nd" prize tier for the X PRIZE for, say, 80mpge cars that really do a good job on the other "mainstream" criteria, but nevertheless I think it makes a lot of sense to focus, as the Automotive X PRIZE does, a lot of attention on a particular important technical challenge.