I could make my BMW more "efficient" if I didn't have the stop start system turned off (automagically) - The reason it's off is two fold. 1) I'm not convinced that repeatedly stopping and starting the engine is actually that good for it. 2) In an automatic, it stops as soon as the car does - so makes parking/pulling out of junctions a hair raising experience.
However, if you have a hybrid, the batteries can get you restarted and the engine can cut in at its leasure. Though it doesn't eliminate the fear of engine failure, it should reduce the number of times it is started and stopped so lengthen the time before it does - hopefully after you've sold it to some other smuck. ?