IMHO whenever there are areas that are prone to dirt build up that promotes corrosion there should be some protection, especially if there is any equipment in the area. The 928 has a splash shield in front of the front wheels to protect the retracted headlights, at the rear to protect the cruise control vacuum chamber and the A pillar ; at the rear the front shield just covers the rear of the B pillar, the rear shield covers the retracting radio aerial . On the other side rear, the front shield covers some fuel system pipework, and a pressure accumulator. These sort of shields are very common these days, and are a good thing. In a P4 it shouldnt be too hard to find a curved plastic something (rubbish bin?) that might roughly fit the curve of the wheel arch?