Someone say my name?
Hello Alex, well sorry to tell you this, but the SPI 2.0l is the worst one to get, and you got it at the worst millage.
The SPI motor is known for dropping valve #4 at around 130-160K, And trust me, IT WILL HAPPEN, I can not count how many SPI owner get around 130-160K and say they dropped the #4 valve.
The Zetec looks like this, and it is the better motor.
Now I know this bit of knowledge might be very bad, but some people do decide to rebuild the head and put performance parts on.
But for you performance questions,
Exhaust? Check out Trubenz.com, just don't go over 2.25 diameter on the piping, even with a CAI from FSWERKS.com would not make enough power for something like a 2.5 diameter. You'd only be losing power.
As far as lowering the car, I lowered my 03 2.3l ZX3 with the Ford racing performance kit, they got two options, you can get lowering springs that only drop the car 0.5, or 1.5, I went with 1.5.
But there are other kits out there too, like Eibachi, and EGR adjustable kits.
And know that I bought the 1.5 inch kit, but after about 3,000 miles it will settle down about another half inch in the front, and 3/4th's of a inch in the back.
Hope this helps, let me know if you got any more questions.