I just got back from Il Cinema Ritrovato 2014 in Bologna and saw the latest restoration of A Fistful of Dollars. Sir Christopher Frayling was there for a few days to give his usual excellent insights into Leone and spaghetti westerns in general and again I got to chat with him.
A quick aside: although there are no definitive original language soundtracks for many spaghettis, personally I prefer to view them in the native language of the principal actors. Therefore English is my favoured choice for all the post-Colossus Leones.
Fistful has now had its English soundtrack restored from a combination of several 35mm and 16mm prints and separate original music, dialogue and effects tracks. As it has had no new sounds added I consider it as authentic as any other in existence, although it is effectively a 'new' track. Naturally, given that the restorers had access to all this original material and could recreate the entire track from scratch it doesn't make sense that they would also create a new mono track just for the sake of it.
I can finally see why they sometimes considerately include a folded-down-to-mono remixed/recompiled/restored audio track for those who prefer the mono experience.
My point is that though previously frustrated at the lack of original mono tracks on BD for some of these films, the concept of such a thing becomes moot. The only way they could include a truly original (in this case, English) track is if they simply transferred an entire, worn and damaged in places, 35mm optical track to BD. Even then, it would likely be missing some audio due to the various different international film edits.
We really do get the best of all worlds now and certainly far better than the original audiences had.