You haven't been to MY local Honda dealership have you? They're more than happy to help but won't wipe a cupholder down without a half hour labor charge.
The Si is
a great car but entirely different from a Mustang. Nothing beats a rear-wheel drive car for performance FEEL.
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.