We may have wandered off track.

The F# chord in 'How great my joy' (when played in D) has nothing to do with muddiness or dissonance. It's simply an unusual sound in a very old piece. The tonality is archaic, and so the chord is not the usual.

Our gang enjoys the archaic and unusual.

D is a high key for this song. We play high to accommodate the flutes and to fit an enjoyable alto line under the melody.

Leadfingers, I'm glad you are enjoying the richness of the modern era, where people looked at the keyboard and decided to use all of those notes.