Question about selling car/buying used one

I currently drive a 1995 Chevy Yukon that is a major gas guzzler, and with the rising gas prices, I'd really like something more fuel efficient. It has about 240,000 miles on it, but despite its high mileage, it runs really well; the only thing that I know is wrong with it is that the air conditioner doesn't work.

My mom says that it would be better if we waited until the car stopped working, donate it (which would get us $0 for it), then buy a used car for several thousand dollars.. But I really don't see how that would help us out. What I think would be better is to sell it now for what it's worth, and buy a used car for several thousand dollars. She insists that the other way would be better, but I keep telling her either way, we're still going to have to buy another car, and with option two, we'll at least get some money for it instead of donating it and getting nothing. So, OT, based on the information I've given, which option would be the better choice?

The money you save on gas buy selling that car and buying another one won't save you anything. You might as well run that car to the ground and just start saving for a new car now.

If you really want to though, you should look up the Blue Book value and see a ballpark estimate on what you might get back.