Hey Tom! That's my car! To answer a post from above - yes they are visually nice by filling out the wheel well, but more importantly for me is that it brings into check the understeer with the factory setup - so that does affect performance in a good way!
With the stock 18's (I use them on the track) I am running 15mm front and 10mm rear. This helps dial out the understeer inherent in the car due to the smaller wheel width in the front and resulting narrower track. My front and rear track are almost exactly the same now which yields a fairly neutral car.
The car is also sitting on H&R Sport springs. There is no rubbing or issues with this setup (stock tire sizes) and car drives great.
I've always used H&R Trak+ spacers and lug bolts/studs with great success! --ch.