Welcome back Lil' Lori!
When you book a 7 night cruise while on board you'll get a $100 on-board credit; that's per cabin, not per person. As a diamond member, you'll get $200 off on a balcony cabin. You will also see and increase in the value of your coupon book. Finally, and most important, you'll have access to the Concierge Lounge! You can have free cocktails from 5pm to 8:30pm.
Remember, you won't have to decide when or where you want to cruise when you purchase a "Next Cruise Booking". It's just a booking number that doesn't expire until you use it.