For a practical car, you can get a normal 4 seater that gets the same gas milage and is a heck of lot more practical. If you were living in Rome where everyone else owned a Vespa (or clone) then the Smart would make sense. In the USA, even in big cities, the Smart doesn't make sense for utilitarian and cost reasons.
If you want cute rolling billboard that is an attention getter, maybe. For a car that is appropriate for kid the learn to drive in? Are you really serious? What happens the first time they drive a "normal" car at college or on travel?
For myself, a small motorcycle gets huge gas milage and has very cheap insurance, tags, taxes, titles, etc. Yes, I like riding a motorcycle and ride safe so, I'll spend $12K on a motorcycle long before I do the same on a SMART (dumb car). In reality, something along the lines of Scion B, or similar Honda/Nissan/Toyota model is a more reasonable choice for the avearge citizen without extremely specific needs (like parking in Rome where you need park in the width of a normal domestic U.S. parking space).
A normal "small" car in the domestic U.S. market will be parkable at shopping malls, college parking lots, etc. so, the ultra compact SMART doesn't really have the same appeal it does in Europe where parking spaces are incredibly small and the roads used to be goat/cow/horse paths and are sized accordingly.
I see the SMART as a novelty in the domestic U.S. market much like an Ariel Atom. A few people will buy them but, not for practical reasons.