For starters, this is a proper application of the template on your car.
Be sure that whatever you do it fits with the look of the car. I question whether the few dollars saved on some weird looking aerodynamic enhancements would pay for themselves in the cost of both time and materials. I also wonder if you'd want to fiddle with the stock look of such a great car, I mean, if it comes down to spending a few hundred dollars more on fuel over the next 5 years or putting some crazy looking stuff like a Kamm on my cool car, I'll pay the money.
Next off, I'm sure that this car has been aero designed to within an inch of its life. I'm guessing that based on its rough shape, MB and Chrysler were scared to death of an Audi TT lift off at high speed, so they made sure there was plenty of downforce. Downforce=Drag.
I'm guessing you have a retractable spoiler that deploys at 45MPH or something, this is meant to break the lift. I see some crossfires have a permanent spoiler which to me looks a lot less prone to having mechanical issues, and has a more efficient shape to it. This spoiler could really help your Cd because it brings the rear end of the car closer to the template. In addition, it will help with what certainly must be a lift at higher speeds. It will probably make your car feel much more planted and stable at highway speeds too. If you can get one of these and put it on you’ll be happy.
There are some hidden things you can do to improve a bit. The grill block and belly pan would be big. Adjust your tire pressure up closer to the highest recommended pressure printed on the tire, I'm guessing that Chrysler wants it at 32psi or so, get it up to 38. That will save you about 1-2MPG alone. Hiding in plain sight would be the factory rear spoiler.
To get the biggest gain in fuel efficiency, you need to adjust "The nut behind the wheel". In other words, your driving habits, this will pay off more than any aero tweaks.
The largest areo drag is caused by the general shape of your car, the air affected by it, and thus the air you need to control extends out many feet around and in front of your car. Worrying about how the air is flowing along the skin of the car has a use in gaining insight on the mass air flow, but tweaking this with anything small is unlikely to have any measurable effect.
So, Block the grill, Add spoiler, Pump up tires, see about cool things you can add to act as air flow diverters around your wheel wells, look into a belly pan. For Petes Sake....Put your dern wipers back on, and never do anything to save a few dollars that can jeopardize your life. Safety First.