I would take the deal if you hate your current car for the problems, but otherwise love it.
The ST rocks. And being upside down on a loan is not a killer. What interest rate are they offering on the deal?
If it is 3% or lower take it.
If they are not offering any low percentage financing, then THAT is where to squeeze them.
Tell them YES IF they give you 0% financing for 60 months
If they offer anything under 3% take it..