Yes, it is about time, given your experience! I really believe that anyone who is able to write a substantiated book on a subject like that for Poser is bound to be successful. Look at the popularity of "Practical Poser". Although there are many Poser communities and lots of tutorials, there is almost no literature, which is a bit of a surprise, considering the popularity of this software and the time it has been on the market.

I haven't worked with Poser a lot since I spend most of my time trying to get a grip on Cinema 4D. With regard to C4D, however, I've worked with professional learning material (DVDs and books) a lot, and I can't emphasize enough how important well-written learning material can be, and how much it has helped my learning curve. 

I think a book on Poser along the lines you are planning to write will definitely find an audience of more than just a few people. Just go for it, I'm sure it'll be well worth the effort and time it takes to release it!

By the way, has it ever occurred to you to release tutorial DVDs instead of a book? Saves the trouble of endless writing... and would be just as welcome, as far as I'm concerned...