As important as fuel economy is--especially skyrocketing prices of gasoline--the overall cost of ownership is even more important. Car payments, depreciation, repairs and maintenance, etc. all contrilbute to the cost of ownership. Before I spend any money on my cars I consider ROI--"return on investment". Only those things that will save me money in the short-term or in the long-term will usually be done.
Because of the miles I put on my cars (which you can see from my garage notes) I decided to keep my cars and squeeze as many miles as possible, and then as many mpg as possible. The article I linked mention idenitifies was to accomplish those things. Take care of your car and it will take care of you.