onshore - It's safe to assume that if you scrape on things with the stock suspension, it will get much worse when lowered. These cars have alot of front overhang even compared to other sports cars, which means that the front end will take alot of abuse on dips and curves. The angle between the road and an imaginary line between the tire and bumper will decide how susceptible the bumper is to scraping.
http://4wdtrailzone.50webs.com/The_Breakover_Angle_explanation.htm
I've got a RoW suspension, I've scraped on driveways, sloping curbs up to driveways and on the occasional dip in the road that they use for water control. There's no way to avoid it 100% of the time where I live. Others may have roads that were more flat or maybe they can avoid these things, but I'm careful and still have scratched the car.
There are products that you can buy, like the boomerang, to protect the bumper if it bothers you.
http://www.************************************************************/product.asp?pf_id=P900015&dept_id=4086