Instead of getting a better MPG car, I moved closer to work. :) I put on around 15 miles/week commuting, doesn't really matter what I drive.
That said, I've always owned at least 2 cars, one of which is an econobox. Because of this, my 1998 van (the weekend fun-mobile) only has 120k miles and will last forever.
Older econoboxes are cheap and disposable, cheap to insure (with two teenagers in the house, that's a BIG expense), cheap to register and cheap to drive. When it's fried, throw it away and buy another used one. No attachment, just a tool.