I remain confident that Tolkien was capable of distinguishing between the aesthetic differences of the Mass celebrated under both circumstances described -- what I suspect he was getting at, besides the likely possibility that both may be valid, is the disposition of the believer, and the danger posed by placing one's demand for a perfect liturgy and experience of the liturgy.
Case in point -- recently I was obliged to attend Mass at a new parish; not one I would usually go to, but it was the only one in the area at the time. Turns out this was one of your more liberal Jesuit parishes, staffed by a priest who managed to use the gospel text of that day -- Jesus' dinner with Mary and Martha, if I recall -- as a basis for condemning Bush's Constitutional Marriage Amendment (don't ask me how, it simply boggles the mind). And those attending the mass were very much like "the usual bourgeois crowd" Tolkien described, underdressed and apathetic.
Needless to say, I was very much preoccupied by righteous indignation over the priest's homily and the crowd . . . and remained preoccupied throughout the rest of the mass. It was only later that I had realized what had happened, that my emotions got the better of me and that my concentration was entirely misplaced.
And I think this was what Tolkien might have been getting at in his recommendation to "make your Communion in circumstances that affront your taste" as a spiritual exercise: What had been for me a provocation to discontent and anger could just as well be a motivation for deeper prayer and reflection, to recognize (and pray for) my brother and sister, even in circumstances that were not to my liking. Definitely something for me to work on in the future.
So, that's what I got out of it.