If you did 3 - 10 day cruises in September it is far cheaper than 3 - 10 day cruises during Summer and Holidays. So, it would never be fair.
Some 10-day cruises are expensive, some are rather cheap. The transitioning cruises are typically very cheap on a per day basis.
Since it is a loyalty program, a person that sails 10 3-day cruises has really returned more often than one that has sailed 3 10-day cruises. And they had to go through the safety drill 10 times so the extra benefits make up for that.
You could also argue that someone that sailed 10 3-day cruises in a 4a stateroom high season could have paid much more than someone that sailed 3 10-day cruises in a 11c low season.
So, I guess they need to do this.
Category 1 - 1200 points per night, extra 0%, 25% or 50% or 75% or 100% depending on season.
Category 2 - 1100 points per night, extra 0%, 25% or 50% or 75% or 100% depending on season.
Category 3 - 1000 points per night, extra 0%, 25% or 50% or 75% or 100% depending on season.
... and so on, so on.
Category 11 - 100 point per night, extra 0%, 25% or 50% or 75% or 100% depending on season.
Bookings made less than 45 days of sailing, with deep discounts - 50% of points
Drink Purchases on Ship: 5 points for cocktail, 1 point for a Coke
Purchases on ship: 1 point per $1
Photo Bonus: 10 points per photo purchase, 100 points per CD in addition to purchases on ship points
Survey Bonus - 1000 points for filling out survey at end of cruise
Disney Transfers - 1000 points per Round-Trip

1 billion points - Free 3-day cruise, a free Shutters photo with the captain and lifetime Double Gold Benefits including 30% off future cruise, 6 gifts, one party with a cheese plate to go, and one shirt, one pair of pants, and one pair of skivvies dry cleaned and pressed.

5 million points - Gold Benefits such as 15% off future cruise, 3 gifts, a party, and a shirt dry cleaned and pressed

2.5 million points - Silver Benefits such as 7.5% off future cruise, 2 gifts, and a cup cake, and a shirt cleaned or pressed

1 million points - Rust Benefits such as 5% off future cruise, 1 gift, and an extra mint on first night, and a pair of skivvies cleaned or pressed

100,000 points - A nice welcome back on a future cruise and Buy 99 / Get 1 photo free coupon.
First Time Cruiser -

Free On-Demand TV (hey, they already do that)