imo, 18's on a 4th gen will look too big unless you're getting a kit (or already have a kit), or your car is really slammed. the 4th gen body style doesn't fit 18's well. again, that's just my opinion.

215/35's will be thin. you'll be riding on rubberbands. so if there's a great potential to hit ditches, potholes, then you might want to think twice.

also, depending on the style of your rim, your 18's could look very 17. and your 17's may look more 18's. more often, rims with a distinct "lip" will look smaller because the spokes will be shorter. now this won't be true for rims whose spokes are a dark color and the lip is HIGHLY polished.

for instance:


will look smaller than these:


if you get them in 17" and compare them side-by-side.

just sharing my opinion. you can take it for whatever it's worth.