It depends on your goals and beliefs. When you say "ecologically responsible", some would say to do away with the car altogether & walk (or bike, or take the train, or????) Economically beneficial? Yeah, owning only one car probably wins that argument most of the time. But the beauty of freedom is you get to choose what you want to do.
I like this site and going for the best mpg I can get because I enjoy the challenge. Not because I'm afraid I'll destroy the Earth if my "Carbon Footprint" is too big, or anything like that. And I may spend more gas testing mods than I'll ever save as a result, but again, for me, it's the challenge. If I really wanted to save the most gas possible as my primary goal, I'd probably get the smallest, most fuel efficient car I could find (like my White Gnat), drive only it, and as little as possible.
So again, it's about what YOU want to do. All of us who answer your questions have a little bit of what WE like to do thrown in. Take the advice you like.....
