There isn't any extra rewards for the completing the whole Reward Book Page.
(But I think, this event is generous enough, we don't need any more reward. I never thought, that I can get so many rewards/trinkets/cosmetics for MP...and the MP reward for logging in is insane! 400 MP for login, 200 for quests and 30 for wins! Every two days you get a Premium Legendary as a gift...only for log in. Unbelievable! Thanks CDPR)