Hello. First of all I would suggest besides posting here, join up on some of the v6 mustang boards. I just got rid of my v6, so I've been a member on one for a few years. I suggest
www.3.8mustang.com/forum/
I wouldnt tell them you want carbon fiber tail lights though.

Those are usually concidered rice (thats a bad thing). If you want to start out with a few modifications, I would suggest a CAI (cold air intake), dual exhaust / underdrive pulleys.
Not only will this help gas mileage out a little, but you will get the cool sound of louder exhaust.
If you want to get more extreme, I would suggest aftermarket gears. I would only go with Ford Motorsport gears though. Right now you have 3.27s, I put 4.10s in my v6. Made it fun to drive, though you have to get a chip to fix the speedometer since the gears screw it up.
With intake / exhaust / pulley you would see probably 15 extra horsepower or so.