Is there anything wrong with the 13 year old car? If not, I'd say thank generous person profusely and ask for whatever amount they were comfortable with giving you for a new car and invest it, and delay buying a car (not brand new, mind you) until such time that the 13 year old car starts having major issues.
If the older car is already at the point where you're repairing it constantly, then suggest you buy a 3-6 year old car in good working condition that gets great MPG. Insurance costs then would be similar to an older car, since you'd hopefully be able to afford car without financing it and avoiding having to carry full insurance on it, and since new cars depreciate the instant you drive it off the lot, slightly older models are usually in excellent condition and a better value, and maintenance costs should be similar to what you're already paying.
http://www.mrmoneymustache.com/2012/03/19/top-10-cars-for-smart-people/Speaking of which...what sort of car are you looking at that requires expensive maintenance?? That's a big "hell no" at even considering if you think it needs more than average stuff like oil changes and tire rotating and things like occasionally checking the fluids or wipers, which you should be doing yourself (I change my air filters, wiper blades, even batteries, but most auto parts stores will install most of that stuff for free if you buy it from them). You don't go to the dealership for anything other than recall repairs (in other words, stuff they have to fix because the car was screwed up by the manufacturer), so if you're looking at something like an Audi or other types of "performance" vehicles... take a giant step back and re-read the above link.
Just because it's a windfall (in the sense that you won't be paying the initial purchase) doesn't mean you go get a ridiculous vehicle that requires more of your money to maintain.