Might i suggest H&R OE springs. I have them on my car and i am very happy with them, I also have 17" wheels and Bilstien Sport rear shocks. The H&R OE springs lower the car 1.0" in the front and 0.5" in the back, very modest, but a noticeable difference, perhaps what you are looking for. The springs have reduced the body roll of my car and maintain a very driveable feel.
With 18's, i am not sure if your tires will rub, but i can tell you my tires never once rubbed, so you should be fine.