
Maybe the answer is that there's more than one way to do it, and different ways are right for different communities and different occasions. I don't know whether you've ever been to the cathedral where I ply my trade, Merseysider, but I hope you'd recognise us as another place where the people get to sing the bits that belong to everyone. It seems to me that me the most valuable role we can play as a cathedral is to provide a model for good liturgy and music. This (for me) means:
(i) doing things the way they are foreseen in the Missal (and sundry other sources - two that I've spent a lot of time burrowing in are the Ceremonial of Bishops, which says how things should be done in Cathedrals in particular, and the Directory on Popular Piety and the Liturgy which is good on how to do things in ways which chime with traditional devotional practice, but respectably!

(ii) showcasing musical items which could and should be sung in parishes that take their music seriously. I like to think that visitors to the cathedral will react to our music by thinking 'we could do that in our parish' rather than by thinking 'we could never do that in our parish'.
I feel a bit out on a limb, for a cathedral music director, in taking the view I've expressed in (ii). Four years ago I went to what was supposed to be the inaugural national conference of cathedral music directors (it seems to have been the last as well as the first), and an illustrious former colleague gave a talk in which he said that if a cathedral musical establishment performed music that could be sung in parishes, it was failing - squandering the resources which should allow it to be completely different from what goes on in parishes. I can't say I agree with that - if the cathedral is to be 'mother church' in a diocese it should teach by example, rather than simply sounding off in a language its 'daughters' can scarcely understand and couldn't hope to speak themselves.
But what about tradition? I think it's a seriously skewed vision of Vatican II to believe that the liturgical renewal means wholesale redpudiation of our musical heritage. It must be the case that the Church still sees a place for the Palestrina Pope Marcellus Mass or the Duruflé Requiem, as vehicles for public, liturgical, prayer. So works like this can't be confined to the concert hall.
Where, then, is the right place for serious art music to be performed liturgically? Churches where they have the resources to attract musicians of the calibre you need to do these things successfully, which mainly means cathedrals. And when? If I could construct a dream scenario for 'my' cathedral, I'd have inclusive participatory liturgies of the kind we routinely have on Sundays and feast days, and then on other days of the week I'd have the choir singing choral masses to congregations of a dozen or so. Add in sung Prayer of the Church daily too - maybe I'd alternate between choral services and more inclusive liturgies. (Obviously I'd have to pay my singers hefty salaries too, to save them having to work nights because they're singing all day.

Why can't it be done? For the reason, sort of, that your fellow MD gave, Merseysider. It's very hard to find musicians with the capability to sing Palestrina and the like (at least with the ease that allows the maintenance of a full-scale repertoire of masses and motets), who also have the commitment to service as musical ministers that accords with the role of the choir foreseen by the liturgical renewal. I'm really astonishingly exceptionally blessed to have the twenty or so musicians who make up my choir, who are there because they do share the vision of these double priorities. But they're exceptional people, and they're not the Tallis Scholars.

So if you can't have a cathedral choir that realises the 'dream' vision I outlined, you can have one, like ours, that goes some way towards it, but has to sacrifice some degree of musical excellence; or you can have a different kind of choir, one that preserves the best of the cathedral tradition, but that has to sacrifice inclusiveness, as a price that (arguably) has to be paid, for being able to preserve and nurture the very precious musical treasures that have been handed down to us. We need them both, I think.
Martin.