The stamps are a back-up. You only need to get one, as iceskatejen posted. They may never check the stamp, but in one of those rare instances that they do (either because your ticket gets flagged or the turnstile computer system goes out) if you do not have a stamp, you will not be admitted.
Ticket every time.
Stamp once a day.
It won't count an extra day- don't worry about things like that please. Put all such thoughts completely out of your brain. They will do you no good, and your energy is best spent on more relevent concerns.
(If I had a nickel for every guest who was concerned that the turnstiles would cause damage to their ticket or that the monorail would stop running halfway through the day- but did not know the name of his/her own HOTEL , I would be a very rich man. Get your horse in front of your cart, people!)