ToddRoh, I am like you, we work all year long and save up for the 1 cruise a year. This year we just happened to fluke out and have enough points to afford the flight. At the end of the day, the cruise is the cheap part, especially if you book with Carnival. For us, it is the flights that are killer. From the east coast of Canada to Miami or Ft. Liquordale it is anywhere from $660 and up per person.
I think booking a back to back would be ideal if you planned 2 years in advance, then that gives you the time to pay for it, the flights, etc with lots of time to spare. Especially if you are like us and like to have everything booked, and paid for in advance, like hotels, car rentals, etc.