I have just spent 4 hours working on one of the books to be re-published on Amazon. This resulted in some polishing and adding about 1,500 words. The extra material fleshes out the original. The book is c. 55 pages/c. 17,000 words. In some ways, a short book is more difficult than a long one, as you have to make your point in a few words. The most extreme example of this scale effect is poetry.