I've just been doing a new arrangement of a piece of string orchestra, based on one of my solo motets. I'm very happy with it, though I expect there will be a little tinkering over the next few days. The problem is that the viola part is truly boring; I have this weakness for static harmony in the middle with a vocal line on top and a moving (generally descending) bass. That's the way it is with this piece; the result is exactly what I want but leaves the violas with acres of the same note.
I've had this problem before and each time I come to the same conclusion, the music as written is exactly what I want. Sometimes I worry that its sheer laziness, that just sticking the same few chords under the melody is the easiest way out. But no amount of tinkering every really comes up with a replacement, too often the more interesting versions simply sound contrived.
So for the moment, my new string piece is sitting on the piano waiting for tinkering. In a few days I'll return to it and see whether I can tweak the viola part to be more fun. But I suspect that I will stay as it is.