Get a nice used, low mileage '09 and avoid the grinning grill and save some money.
Seriously, though, it's all in the math. Never, I repeat, never let a dealer talk you into just taking your car and extending your monthly payments to put you in a new one. That's almost always the worst deal possible.
You want to know your present car's value. You are blind otherwise. Use Kelly Blue Book or NADA Used Car Buyer's guide. Be honest with yourself about its condition. Then hold that info to yourself for the end of the negotiations. Get the dealer invoice info from Consumer's Report. You can do that on-line for just a few bucks. That way you know the initial markup the dealer has. He will also get some incentives, but that is beyond this discussion. Follow Consumer Reports directions on dealing.
Negotiate with the dealer without mentioning any trade in at all. Get them down to their lowest discount BEFORE you even bring up your present car. Then, find out what they will allow for your present ride as trade in and compare that with the trade in value in Kelly or NADA. That's the way to see what kind of deal you are really getting. Chances are that you can get close to book trade in and get close to or even below dealer invoice if you time things right.
Only then should you move the discussion to monthly payments. Know what your bottom line, drive it away cost, including tax is going to be. Then explore interest rates and length of note, which will, of course, vary depending on what the market conditions are and what your credit rating turns out to be.
Dealers are hungry now. Cars are sitting on lots a long time. Don't be afraid to walk away. Don't ever let the dealer know you really like a specific car. Keep talking about Evo's and Subies. Be skeptical about the color, even if it's the one you REALLY want. I shopped 3 different Mazdaspeed dealers in three states before finding the best deal. Don't go for any dealer add-ons or other tricks that change the sticker price. I repeat: They are hungry. Take your time.