My thoughts are that the car/plane concept is one of the most impractical concepts in aviation. Not being noted for being practical, I'd like to have one just to be able to wheel it out in the field and go.
However I do see great possibilities for both military and those living in remote areas, but not for flying into or even near urban areas. Using one in urban areas with the traffic and parking would not be worth the risk. I'd also have have some very strong reservations of leaving one in a parking lot for and afternoon and then taking to the air in it without a major inspection before flight.