Keep the Honda and forget about a Mustang. The Honda gets better gas mileage and is certainly a great car. The only thing which might be better about a Mustang would possibly be the feel of the shifter.
The Honda will certainly require fewer repairs and your car is not even broken in yet. Enjoy dreaming, but spend your money more wisely than on a new car you certainly don't need...as you already have a great car. Also the service departments at Honda Dealerships are much better at treating their customers properly than Ford Dealerships.
Uh, the 2011 Mustangs have been on lots, what, a month? How can you determine the honda will require less repairs? Apparently you have magic powers and can see the future. Perhaps you could use some of that magic and conjure up some common sense. My parents had nothing but grief from the Honda dealership(s) they visited to service the poor excuse for a car they owned -accord.