I'm from a racing/fast cars background; I own a '95 mustang GT and do enjoy speed.
I've also liked efficiency, in lifestyle and the home, for my whole life. I started my folks on recycling, and loathe waste.
I wanted to get a car for FE for awhile; finally had the cash at the right time. Now I don't drive the mustang enough to keep the battery charged.
I think wanting to practice what I preach plays a role - I'm a high school science teacher, and I can't tell my kids to conserve if I drive a sub-20 mpg car. It's also expected for a Physics teacher to be a bit weird, and my car is that! I still drive the mustang to school occasionally, which they all love seeing.
The only other thing I can attribute is my age - turning 28 this year and I have a 1 year old - I don't need to drive crazy or fast anymore. I don't need to compete with other males out there for speed. I have better things now.