I am an employee at a Hampton Inn in TN and want to say that in reality the only difference with Gold and Diamond member status is that as a Diamond member you get a reservation at any Hilton property if they are sold out as long as you use the 48 hour advance notice. Remember though these reservations have to be made through the Diamond desk not the hotel itself. I get several calls every day from some Diamond member demanding they have to have a room that night and that since they're a Diamond member I've got to do it. BUT the call must be made 48 hours in advance and there are certain black-out dates that this does not apply. For example here in March and August we have black-out weekends for the Nascar race. Which means even if you're a Diamond member you are NOT getting a room.
There are no additional snacks, no free movies, different breakfast, etc. Diamond members also don't necessarly have first priority over upgrades either. I personally tend to upgrade Gold members as often as I do Diamonds. Gold members need some love too.