I enjoy the few callbacks to the show, but as several others have said, why not focus on a new slayer?! I always thought that would be a great way to reboot Buffy as a tv show, without actually rebooting Buffy. Focus on a new slayer, there are thousands now, of all ages. You could easily go back to middle school or high school, and come up with all new metaphoric demons.
For the book series, they can easily throw the Buffy logo on the cover to indicate it's part of the same franchise. I don't see many fans going out to buy this. I'll admit I am curious to see where it goes though. I'm guessing they can't take it too deep, since it is for younger audiences.