Paul,
Indeed there are many cars reaching up to 40+ that have more seats in them, when it comes to life, we have no kids,
no dogs anymore, thus our cargo load is limited to the heavy wal-mart grocery day, or my need occasionally to test the
limits of what I can put in the smart for a work project.
I think for folks with kids, or greater need to haul friends and family it might not be a great choice over a 4 seater, but
I have a 16.5 foot extend and climb that fits behind the seat, can put my hepa vac and all kinds of tools, compressor and
materials for exclusion and since that is my main game the idea of fitting a live or dead skunk in there doesn't arise.
I did however transport 2 litters of newborn skunks 2 weeks old maybe, in a large porta kennel (lab dog sized) in the back
of it earlier in the year.
The occasional rock squirrel capture, no problem, gophers, all day long!

I can do pigeon jobs out of it to, again as long as either single story (16.5ft. ladder limit) or roof access at commercial spots.
Insurance is about $40.00 a month and our financing since the smart is a mercedes like the sprinter was nearly 0%.
Now combine that with what Ron said! Man this car flies, when my wife is allowed to drive I feel like I need a blindfold!
Our work is mainly using the interstate to move 2-3 hours north and south and the posted speed is 75 MPH which of course puts
everyone at 80-85 MPH and the smart goes all that and then some, actually is one of the negatives for me, in the sprinter
I don't watch the speedometer just set the cruise to 75 or 70 to conserve on mileage, but with the smart, no cruise in our base
model so sometimes I look down and realize, oh (blank) need to slow down!

Love the car, the space really doesn't limit me at all, and 5-6K for 4 seats instead of 2 wasn't a priority for our particular lifestyle.
I think after the expendables 2 comes out, and Arnold in all his massiveness is speeding around guns blazing, more folks will buy
them, much like mini coopers and the italian job, or the fiat as Ron said, fun to drive!!!
And of course, safe too!
Justin