What is wrong with the one-per-part concept? I actually prefer it (or at least some as-few-as-possible-per-part concept), and as much as I BTW enjoy Werners recordings, I have to say, that I think the music in hands like Richter's often turns into some kind of unwanted "mass movement".
Dear pe-zulu (I'm glad you are back

)
There is really nothing wrong with the one per part as far as my taste goes. I do not believe that Bach usually had only one singer per part, though. The argument (as by Rifkin) goes that there are only one set of parts, but then it is very likely that two singers or players used the same sheets of music. Bach's memo to the Leipzig council suggests he would like to have more than one voice per part.
That said, I now try to judge music by results alone and not by conceptual considerations. The way I see it, there is no possibility whatever of bringing back the way the 'original' thing, so we would rather appreciate the music without too much thinking about how it was played.
Nowadays there are so many schools of interpretation of old music that I find I can only find my way through the score itself. For this, historic knowledge is important. But music is too much alive to be put into a kind of museum. I am stating nothing new, as I already said all this before, in this forum.
For Bach choral works, I find it that the only works which definitely require a bigger chorus are the passions, because of the turbae effects. But in the latter cantatas and perhaps also in the great mass, I think a more historically correct version would include perhaps two singers per part (in the rippieno).
The Dona nobis pacem in the Mass is a very good example: ought we to play it majestically as both Richter and Gardiner do? Or as a rapturous moment, as the Cantus Köln musicians do? Both approaches are fine by me. It is true that Richter smacks too much of romanticism, but that doesn't really bother me: I like Bruckner and Brahms. And the Cantus Köln smacks too much of the urgency of contemporary living, which I really do not think existed in Bach's time (it may have been fast, but it was extremely curvaceous and quite unlike the almost abstract way of contemporary living – the machine-like abruptness of Rinaldo Alessandrini's interpretations is, I think, completely wrong even if it works very well). Anyway, we cannot possibly know.
In truth, I find it it all depends on what one wants to convey... The one voice per part is clearer and more intimate, and also more expressive. The bigger choir is more impressive and majestic.
So I am becoming less and less fussy about rules for interpretation. The only think I truly do not like is the Bernstein watch Me approach or the appalling nothingness I found in a set of Bach organ DCs by Wolfgang Stockmeier I purchased some weeks ago.