Don't knock Westminster Cathedral. Two points in their favour:
(1) I go out of my way to go there whenever I am in the area, which is more than can be said for St Hernia's on the Mount Without. So do a lot of other people.
(2) There are more people there for weekday Vespers than at any other church I know: more than at many monasteries (including the community in the count). Their advertising it as Vespers rather than Evening Prayer may have something to do with it. The two names mean something completely different to the uninitiated.
Any time they want to swap their organ for our elderly parish toaster, I'm all for it.