As both Andrea and Bhagat said, your coils and your struts should match.
Your struts are designed for a certain amount of travel and a set stiffness
in that range, changing your coils screws up what the struts were designed
to do.  Not to mention all coils are NOT created equal.  Most manufactures
will sell you a strut/coil combination for any amount of lowering you want
to do.  Check Koni and Tokiko for ideas.

No first hand experience but from what I have read, Andrea is correct.
Lowering the car does very little for handling and makes for a scraped up
front bumper from driveways.

I added standard height Tokiko HP struts to my car and they help the
handling a LOT.  Front tower strut brace also helps, but makes the car
stiffer so you pick up more rattles.

Before you go spending much more money on upgrades do some research first -
the best place www.dsmtuners.com
or vfaq.com.