From a financial standpoint it's almost always best to drive a vehicle until the wheels fall off... OK, maybe sell it just before then.
Saving gas is certainly a noble goal. Have you done the math on how much gas you use, how much gas you'll save, and how much money the new vehicle will save?
I have a good bit of gas-guilt driving my Trooper. It gets around 17 mpg. The Mazda 3 wagon I'd like to have gets around 26 mpg. If I drove 15,000 miles each year the Trooper would use around 882 gallons. The Mazda would use 576 gallons saving 306 gallons per year and at $2/gal that's $612/year saved or $51/month.
The problem is that my Trooper is only worth around $7500 at best. The Mazda 3 will be right around $20,000. The payment at 6% for 60 months on the difference would be $241.66... $190 more than the cost of the gas (Yes, I know there's more "cost" of using more gas than just the money - no need to lecture). Right now I only drive around 7000 miles each year so my useage is much lower. My next vehicle will be more efficient, but with only 75K miles on the Trooper that purchase may be a long time in the future - it's the most reliable vehicle I've ever owned.
Try the 3... it's amazingly BMW-like for the money!
