One thing to keep in mind with Goldpoints is that they come off the cruise fare before some of the other discounts. I believe they come off before SSS and onboard discounts (I may be wrong as it might be one of these two and then TA discount). Therefore, instead of saving $400, you would save only $361.
Therefore, I am saving my goldpoints for cruises that don't have these discounts such as three day cruises or cruises that don't qualify for SSS savings.