I have Eibach springs and the car has been lowered under 30mm front and back. It looks just right. I never got the wheel alignment done at that time (almost one year ago) because everyone told me you can't adjust the camber on an Alfa.
The tires got overworn on the inside. You can fix that by rotating the tires between the wheels.
I got the wheel alignment done a month ago (maybe sooner) and besides a small error the mechanic couldn't correct ("because it's italian") - something on the right side, a small matter anyway - I had no problem whatsoever.
If you have sufficient "cash" try to get a full coilover suspension - KW V3 - which will give you more posibilities to "align" your wheels.
Also, changing the springs with shorter ones will slowly but surely kill your stock dampers. You should change both of them.
Jeremy Clarkson on the Brera: “Think of it as Angelina Jolie. You’ve heard she’s mad and eats nothing but wallpaper paste. But you would, wouldn’t you?”