One of the best small concept cars was the VW Scooter cabin thingy, clearly inspired loosely by KR200, but this was 30 or 40 years ago. Since then there have been scores of bubble/micro concept cars which have got no further than motor shows. They are designed to tease us into thinking there is new stuff around the corner, and to get good publicity and kudos for the company.
Out of scores or hundreds, we did finally get Smart cars, and their success HAS made a few people realise that it is not necessary for a lone commuter and his/her lap top to travel daily in a huge executive barge. Daewoo, Toyota and a couple of others have also had modest success with small cars, but none of them has looked like any concept cars or shared a single component with them, so as far as I know virtually every concept car has been a dead end, and therefore a waste of money and resources.
However there is one fundamental flaw of the Smart car: it is a one trick pony: only 2 seats and room for a sponge bag! We have a Suzuki Wagon R+. It is only very slightly larger than the Smart, has more power, can carry 5 people and a reasonable amount of luggage, or 2 people, drum kit, geetars and amps, or two people, picnic and Drum Car. It's better on motorways and long drives, slightly more economical, easier to service.....
.....and.....
..... our top-of-the-range one cost...
....less than half the price of a Smart Car!