I generally don’t evaluate manga based on the quality of the extras available, because they vary so much from publisher to publisher and book to book. Sometimes those sidebar messages from manga-ka are fun, and sometimes you get Yû Watase providing a release schedule of anime, soundtracks, art books, and other products based on her manga. (Short version: “It’s all awesome!”)
I know those sidebars aren’t really intended to be deeply informative or uniquely insightful. They’re around to fill the spaces in the tankoubon where the ads ran in the magazines, and possibly to generate a little rooting value by having the manga-ka speak directly (or “directly”) to the audience.
The content is generally pretty repetitive. They’re working really hard, and they’re sorry they’re behind on their fan mail. This volume isn’t as good as they’d have liked, but they’re trying, and reader support keeps them going. They wish they had a kitty. That sort of thing.
Sometimes the manga-ka will slide a little insight into the mix. I remember the bits from Ultra Maniac amounting to what was essentially Wataru Yoshizumi’s very polite take-down of the process of adapting the manga into an anime. (“Well, it really doesn’t bear much resemblance to the comic I’ve created, and I don’t really understand the choices you’ve made, but thanks for the extra income!”)
Ai Yazawa’s back-up strips are always a pleasure. I love her repertory-company approach in the “Junko’s Place” strips in Nana, with the cast sort of hanging out and bickering over their comparative popularity levels. The strip in Paradise Kiss where the characters break into Yazawa’s apartment and steal her clothing is a particular favorite.
I also like Minoru Toyoda’s little mini-summaries in volumes of Love Roma where he talks a bit about his creative process – what made him want to tell a particular story, or what effect he was trying to achieve with an individual chapter. And I’m crazy about the continuing struggles of the S.C.D., an alliance of one-appearance characters who are scheming for greater visibility.
But for me, the undisputed ruler of creator talkback is Emma’s Kaoru Mori. Wikipedia informs me that Mori is “famous for her unflattering self-portraits” as much as she is for her incredible storytelling, and I can believe it. While I love the serenity and emotional detail of the manga, I’m totally enamored of the fanatical enthusiasm Mori portrays in those after-chats. (Mely provides an example at Coffee and Ink.) CMX kindly sent me a galley of the third volume of Emma, and Mori’s remarks begin with the disclosure that the chief editor of Beam described her as “a ‘weird woman.’”
Well, duh. That’s the fun of it for me. While the release of watching Mori run rampant isn’t necessary to enjoy the story that precedes these bits, it’s still great fun. I could read a book that consisted of nothing but Mori’s after-chats.