Let's see if it actually results in price changes. Currently - at least on Amazon - many ebooks seem to be priced either just above or just below the paperback equivalent; there is no clear "20%" factor involved. Will they become 16% cheaper from December? I have my doubts.
I suspect it's more likely that between Amazon and the publishers, greater profits will be retained.
As to buying more books, isn't my backlog of as-yet-unread books big enough already?