That all depends upon how often you need that extended range. If you need it once a decade, is it worth carrying around all that extra weight and displacing all that cargo/passanger space all the rest of the time? I would say not.This is the beauty of the Volt design. You don't need to deploy vast networks of chargers to quick charge. At some point, you have to ask the question, how much effort and money is it worth not to from time to time burn a gallon of gas. Leaf owners, when they ask me when I bother to lug around an engine I don't need very often get this reply: "because I'd rather haul around an inexpensive engine that gives me limitless range when I want it, than a battery pack that is twice as large as I need it to be and a lot more expensive that have limited range"
If you need that extended range twice a week? Yes, I would say it definately is purely from a convenience aspect (although one might also say sending just a little bit of money out of our economy and into the hands of our enemies is still too much).
If your driving patterns allow you to avoid the gas engine, you can easily use a skateboard design freeing up a TON of room for both passangers and cargo.
All that aside though, the drive free forever really isn't the case IF you want your car to last as long as possible. Quick charging the Model S is generally not recommended for longevity of the batteries. Doing it once in a while is no big deal, but doing it all the time, I would guess, could shorten the battery life.
I would like to see Tesla add, or allow other companies to add some L2 chargers to their supercharger areas.