One of the downsides of listening to the audiodramas is that it's hard to get a sense of change from book to book. Since they're necessarily abridged, every audio is like the best version of the story with all the least interesting bits edited out. I suspect that's part of why there doesn't seem to be much change for Peter from "Strong Poison" to "Murder Must Advertise." There's a little in "The Nine Tailors" but, like you, that book didn't impress me much. But "Gaudy Night" - wow that one is interesting. Makes me want to find an unabridged copy somewhere.

One of the other downsides for the audiodramas is that unless I'm wrong, and I don't think I am because I have a pretty good ear for voices, they keep changing the voice actors from story to story. Peter and Bunter remain the same but Parker and Harriet change, among others. Anyway, all of that is to say that I doubt I'm getting as clear a view of Sayer's writing from them as I might from the unabridged audiobooks. On the other hand, even the least interesting stories seem to move quicker when they're read by a full cast.

I know very little about Sayers outside of a few minutes that the series "A Very British Murder" spent covering her. She sounds like someone who would be interesting to read about in and of herself.