This is very interesting. I quite see your point, bookworm, the whole thing hinges on the rules being written around "Reported RVR" or "Relevant RVR", when there should be provision for "Observed (by crew) visibility". I don't have much to add at this point, and I'm still happy (for now) with my earlier answer. However, I'd like to see the discussion continue, so I'm posting this to keep the thread alive.
Some will act on their observed vis. and required visual references, others will say the regulations specify reported RVR. In UK there is the extra barrier of the "Absolute Minima Procedure".
Lets have some more opinions.