Even my distinctly non-performance C4 has a noticeable difference between standard diesel and V-Power - remarkedly so. Plus it guards against injector failure, which you definitely don't want in a diesel as many of them get seized into the head and have to be drilled out.
Had that problem with a Vito years back at the company I worked for - cost a feckin' fortune to get sorted. Mind you, they were utter junk as most Mercs of that era were. It rusted itself to pieces in the end, as did the other one we bought at the same time.

