The guards can leave marks on the chrome. It depends on how tightly they were installed and whether they ever served their purpose (any impacts). If the guards were overtightened, there is some possible distorting around the holes that is possibly better left covered.
I do think re-chroming over holes is a mistake. I've seen it done and it almost always ends up revealing the previous work over time. The chrome seems to shrink up around the repair. It's sort of a hit-or-miss thing as I've heard it is possible to chrome over a hole without it showing, but very, very difficult to achieve. The fact that the chrome may reveal the repair over time makes things even trickier.
My personal feeling was that I have a US-spec car, so even though I prefer the look without the guards, my car does appear as it originally did. Plus it's hard to justify the hassle of finding bumpers, having them re-chromed, then hoping they'll fit properly. You may be surprised at how bumpers and the cars to which they're being fitted aren't necessarily a good fit. Chalk it up to panel changes, dings and repair work in any of the aforementioned pieces.
Douglas Kim
New York, NY
280 SL #016220