Ed, I haven't read your book, but I have an opinion on the mature themes. I guess the people who have the money to buy much (non-core) RPG stuff are in their late teens or are adults anyway, so I guess you shouldn't sacrifice your story's integrity for a minority of customers.
In my gaming group, the youngest is 22, so we can pretty much do games as we like. While the mature themes are not the main focus of our stories, I have no problems describing succubi acts or gory combat. Text (or speech) has never the same impact as pictures, so I guess if there's no explicit pic people won't complain. Personally, if the BBEG I'm facing acts like a BBEG from the old batman series, I won't get much into the game.
I live in Quebec, and we don't have the same issues with sex / swearing as in the states (we kicked religion out of our moral lives some 30 years ago), so maybe that's why I think that way.