I agree with you to a point. Particularly in this day and age of fuel prices as they are, its not just the cost benefit in so much as to how long it takes you to recoupe your cost but also the 'virtual' value if you will that it would add to your vehicle.
If such a system truly worked and you could gain 25-50% in fuel economy, that makes that vehicle much more appealing to others whether or not you have personally recouped the expense.
This is why the prices of such vehicles like the Geo Metro have shot up considerably. Ive seen early 90's models going for several thousands of dollars and they are being bought up left and right, along with others in that class and fuel economy rating.
How long will it take them to recoupe their expense of a 25+ year old vehicle? They care less about that in particular than they do in being able to say "Im getting 40+, 50+ mpg". They will probably recoupe their expenses faster on a dollar to dollar fuel cost comparison, but it often matters more in their mind that they have personnally take some 'action' to combat fuel costs. That same person, typically, would drop that metro like hot potato if fuel prices fell through the floor and went back to around the $2/gal mark.
