I just lowered my 09 Touring w/out sport package with H&R springs. It knocked my alignment out enough I felt it necessary to replace both front and rear setups.
From my personal experience and reading the lowering thread at
DIY: 370Z Lowering Spring Install it varies car by car and person to person. How much variance are you willing to accept from factory specs, etc.
Read the thread on lowering and you'll find a variety of options. I could feel a real change after lowering. The car griped a whole lot better but I'm not willing to sacrifice tire wear. You will also have to adjust your driving a bit if you've never driven a car with such little ground clearance. It can be challenging!
I have fun driving but I'm not tracking my car on Saturday's or drifting on Airport Rd. I went with Kintex to get my alignment closer to spec. I just bought a set of SPC toe bolts because the camber is still outside what I want. The SPC rear camber arms have a greater range than the Kintex though I'm not sure the 1/2 deg difference would have been enough to avoid using the toe bolts and grinding out the holes.