We bought the car with over 90,000 miles on the clock, and it now boasts over 220,000, and the engine has never been opened up, the transmission has never given us grief (though we service the tranny every 20K. We get a consistent 23.56 mpg and always use regular fuel, changing the 10w40 good quality oil every 3K miles. The only mechanical problems in ten years have been a malfunction in the aftermarket remote locking/alarm system, and a pesky serpentine belt that has left the scene of the crime twice in ten years. We're now looking at changing gaskets and hoses because it's a regular thing.
This is a motor vehicle, and I'm not feature-driven. It just doesn't break down, leaving us out in the middle of Nevada. I would have to say the comfort. The car's name is Mustafa....
I can't think of a way to improve a ten-year-old vehicle other than upgrade it, which Chrysler has already done.