As much as I want to affirm Sayers's understanding of work, I can't quite assent. Yes, there is something dignifying about work, and yes, it absolutely should entail "the full expression of one's faculties."
However, I jump off when Sayers writes that work is "the thing one lives to do." There is a structure and set of goods that fall outside of work on Sayers's account that isn't simply concordant with the good of work, but transcends it. The goods of family, friends, and church all make strong claims for precedence when their pursuit is incompatible with the pursuit of work in the way Sayers describes.
What's more, none other than C.S. Lewis disagrees with Sayers. In the little known essay "Our English Syllabus," he affirms the following by Aristotle:
'We wage war in order to have peace; we work in order to have leisure.' Neither [Aristotle nor Milton] would dispute that the purpose of education is to produce the good man and the good citizen, though it must be remembered that we are not here using the word 'good' in any narrowly ethical sense. The 'good man' here means the man of good taste and good feeling, the interesting and interested man, and almost the happy man...Vocational training, on the other hand, prepares the pupil not for leisure, but for work; it aims at making not a good man, but a good banker, a good electrician, a good scavenger, or a good surgeon. You see at once that education is essentially for freemen and vocational training for slaves.
Lewis is writing in a slightly different context than Sayers, but his basic point is a direct contradiction to hers: regardless of how expansive and accommodating we make the concept of work to human nature, it is always for the purpose of leisure that we work--and not vice versa.
Framed a different way, for Lewis, the sabbath is not for the sake of working more, but for its own sake--and work for the sake of it. It is the sabbath that grounds our activities every other day of the week, and never vice versa, for the sabbath orients us toward the rest which we shall have in heaven and the leisure which we shall enjoy there.
Lewis doesn't go there directly, but he should, as framing work in this way avoids the troubles that Aristotle's account runs into. Either way, the basic worry remains: work simply is not the ultimate end for which man lives, but that by which he lives as man in community with God and His people.