Thanks for your input, everyone. You have all made some good points. I was unaware that fluff books didn't sell well but I suppoes that makes a lot of sense, as unfortunate as it may be. Fluff books retain their value and I always want more, especially physical copies but I would settle for pdfs if I had to. It's true that game master advice is spread out in various books, sometimes featuring fairly large sections, but there hasn't been a book completely dedicated to it. There are so many interesting things you could put inside that book, such as how to design shadowrun campaigns in more depth, guidelines for maintaining a good pace during sessions, how to handle black market shops, actual details on the fencing loot (a huge topic for ages), fully made safehouses ready for play, rules for creating custom gear such, proper rules for creating drugs (Chrome Flesh was on the right track but it missed the mark badly), etc. There are tons of awesome things you could put in that book, I can't imagine not buying it. It could easily have a large amount of crunch.
The Stuffer Shack book would be an automatic purchase for me. I would love to know more information about actual products in the world. I can make up as many as I want but I would rather have more immersion and actually know about brands of soda, potato chips, chewing gum, cigarettes, etc. It would be a roleplayer's dream. Yeah, I know a lot of people wouldn't buy it but this would be amazing for people like me. It would also be useful for the writers too because they'd actually have a nice reference material, right now this sort of information is smattered about in every nook and cranny of the shadows. Even if it couldn't feasibly exist as a pdf, would any of the writers like to take this on as a service to the community? We could have it added as a free resource in the download section of the main website, in the same token as the Big D's Will. It would be a bit of a project to scour all the books but it would be really awesome in the end!
And one thing I'd like to note about fluff books, Attitude continues to be amongst the most expensive Shadowrun books on many websites and it's a softcover. So there has to be some interest, right?

Anyway, I will buy ALL useful fluff books, give them to me! =)