I have been thinking this myself recently. I just got back from a long drive (Brighton to Lincoln) and had to take it steady for mainly financial reasons. In my old car, I would have gotton about 65mpg. Today, i did 38. Driving on motorways, especially now every inch is being watched by big brother's anti speed brigade, is dull and may as well be done in a 1.2tdi. Driving round any major town or city is the same. Power is largely pointless. If i lived near the south coast or drove up an down motorways regularly, i would have an eco box.
However, i live in a very large county that is sparsly populated. There are terrific driving roads near me and i can (safely) enjoy my car. Traffic often bumbles around here so plenty of overtaking at speeds often completely within the law.
One day, there will be no point to it. Not because the fuel will run out, but there will no space and no rural parts left. But i hope to be long gone by then!