Well, the Kindle Scout route wasn't to be for this book.
Which is fine! The only failure is failing to try. And I tried. Now I have the opportunity to follow other routes.
Heartfelt thanks to all my friends and companions of Chronicles for graciously supporting me in the attempt. And thanks again to Brian for allowing me to post this thread.
So what have I learned about the Kindle Scout process that could help other authors who may be considering it? Not a whole lot, unfortunately. Amazon keep the whole thing opaque, which perhaps is how it should be. Anything I might say about why a book is or isn't accepted would be pure speculation. My takeaway is that it's best to regard it as being like any other publisher submission - a shot in the dark.
Submitting itself is a piece of cake. Fill in a few boxes, upload the book and images, then a day later came an acceptance notification then a couple of days after that the campaign began. You get a page which tells you how many views you've had. And that's it. No indications as to how well or badly you're doing, no clues as to how many nominations you've had, no feedback at the end. There's a 'hot and trending' list but what makes a hot and trending book is anyone's guess. It might be worth noting that 80% of views came from the Amazon site itself rather than external sources such as forums (like this one) or social media, blogs etc. hence the book's fate was ultimately in the hands of interested readers (and Amazon's editors of course).
I feel like I should write something else here but my mind has gone blank. Or maybe there's nothing more to say. I came, I saw, I got rejected.
Losing is learning.
Thanks, everyone.