I helped a friend do his mk4 golf recently,
He went for 15mm items and its now very close to the bonnet!
I recently had a "whoops" on a speed hump i miss judged, It was not the sump at all that came into contact, It was the front edge of the sub frame, so for me they seem pointless.
I also read a thread on E38 regarding vibrations caused by these not being fitted bang in line, Although the car we did was fine i will not be doing mine,