It sounds as if what we are looking for here, if we consider all the wishes so far, is a full-blown Content Management System. (The death of professional translators - the more you translate and add to a CMS, the less you have to translate in the future)
Something of this ilk would certainly bring advantages like reducing duplicate/multiple entries and automatic or semi-automatic tying in of alternative data, eliminate redundant data and would attach relevant input from multiple users to existing entries with very little user-effort.
Anything like this in the pipeline?
Er...
The whole data structure already sits in a massive Content Management System that was developed especially for the site. There would, I suspect, be no other way that the site could operate.
AditNow thus comprises about 250,000 individual pages generated on-the-fly by the CMS, including the forum and the events calendar etc..
Mines exist as data objects, with all their data attached to them, i.e. locations, descriptions and so on, *plus* the albums - which may be tagged to more than one mine for the (rare) occasions where an album might straddle two mines (for example, Croesor-Rhosydd trips and Foty/Bowydd).
Users are similarly data objects, as are albums, photographs, events, documents and so on.
All these can be inter-related, for example, photographs belong to an album, which belongs to a mine.
All primary data objects (ie mines, albums, photographs and forum topics) can be set to a security level, which governs who is able to view them.
As might be imagined, this is monstrously complex and given the amount of inter-relationships between various data objects, it's not necessarily possible to make any big changes as this could have unintended consequences.
Turning to your penultimate paragraph: yes, it's possible to create a duplicate entry, thus the responsibility rests on the user to check that the mine is not already in there. Whilst there is the possibility for duplications, these are usually picked up on quite quickly.
Hello again darkness, my old friend...