I agree with Rainboe - The science of recognizing and reporting a cloud base isn't all that great and "mother nature" doesn't often agree to make no changes. In the US, the requirement has been strictly RVR for quite some time - however, the US military had stubbornly maintained the DH/MDA and ceiling height issue for some time. Now they also recognize the futility of such a stance and use RVR.
The only thing I would point out is that there are a number of "new" instrument approach procedures being developed - and the ability of the pilot to see another aircraft involved in one of these newer procedures may come into play in a way that we may not be aware of at the moment.