if its the same loan length, its only an extra $360 in difference between the last loan and this loan.
The biggest difference here though is the 12 payments you've already paid and the down payment. I can't imagine whatever number that comes out to being very pretty. You'd just have to think about whether that comes out to is worth the extras.
That being said, and being a car salesman, I'd love to have you as a customer
Too bad I sell Hondas....