While I have no evidence to prove this other than my own findings, I just purchased a 98 E300D with substantial undercarriage rust. Of course the car had no panels when I got it. 177K, and a NJ car. I would like to believe that the panels if in place would keep the splashing of road salt off of all the engine compartment fittings. A/C connections rusted, oil cooler lines rusted, brackets for intercooler tube rusted, brake line holder brackets rusted, etc.

No way for me to know for sure as I don't have anything to compare with, but I have my work cut out for me stop the corrosion and then prevent it from recurring.

Just my thoughts about the panels' value.