I've considered my own situation, and cannot foresee a substantial reward for giving up my gas guzzling SUV. I'm a city dweller, and drive around 10k miles per year. If my fuel efficiency trebled, and gas prices increase $2/gallon, I'd be saving around $1,000/year. Considering the concessions I would have to give to gain the fuel efficiency, no way.
Well, we needed to be looking for a third vehicle anyway, as I have two teenagers who require mobility. Their mom and I are tired of chauffering them everywhere. Our conversion van has been relegated to around-town errand-running and extended vacation trips. For us, the decision made sense; your mileage may vary.