I think one of the main points of Wagner's ban on ensembles was that they take too much emphasis off the words and make them unintelligible, and indeed the maidens sing mostly in turn, and when they sing together it's for a very short duration or without words.
I believe it was common for audiences in the nineteenth century to have the librettos to hand during much of an opera performance (though not sure if this was as true of Wagner opera-goers as those who went to other operas), so issues of whether all the words could be heard were perhaps less important. I don't know what Wagner thought of Verdi's brilliant ensemble writing (often real highlights of his operas, something I miss in Wagner, who wasn't, in the Ring at least, so good at portraying interactions between more than two characters) - anyone know anything about this (I imagine he would have criticised them)?
