In practice, you will receive great feedback from a very small proportion of the students (and this subset will consist almost entirely of students who will do well on the course regardless). But even the weakest students can and will make perspicuous observations, or point out gaps in your explanations, that will be helpful. And then many students will be hard-pressed to contribute anything.
If any credit at all is traded for feedback, you actually raise the threshold for students who are aware they are not among the top and hence afraid of saying something dumb. The "swots" might go into overdrive, which generally produces lots of great feedback, but you feel you are abusing the time and kindness. The majority who has no substantial thing to contribute might feel compelled to manufacture something.
The "extra" idea does not mitigate against the latter problem, since students will evaluate every bit of possible credit in terms of the relative effort. Any carrot being dangled is far play.
So: my answer based on experience over several books and years of teaching: do not skew or degrade the feedback you could be garnering with any of these extra credit arrangements (quite aside from ethics which has been well addressed in the other answers). Use the book-in-progress as lecture notes, make it very clear that you are aware it is still teeming with mistakes, and that any and all comments are hugely appreciated.
At the end, you will know the main feedback contributors by name. They will come to you for recommendation letters, career advice, and so on. And then you will be able to reward their kindness in kind. Such is not a bribe; the praises you have to sing about such a student are genuine!