If you book onboard with cash you get the 10% reduced fare and only have to make a 10% deposit, plus you get OBC.
If you use points you do that, but also have 3 days to call DVC to convert it to points to get a reduced point amount. I think it is 10%. Any fees/fares have to be paid on that date.
We did not know which cruise we wanted to do so waited on our dummy date. When we did decide (from May to Sept) we got reduced points but not the full 10% off. We used points for the adults and paid cash for dd.
How it works-They refunded the original deposit and charged the new fee for dd.
What they say-
The advice given is usually-- it is a better value to use the points for hotel rooms. If you do use points- pay cash for the 3rd passenger on. So know when you might want to go and the points involved before rebooking.
However, you can not make any changes when using points without paying the fee so make sure you know which kind of room you want. Also you can not change the points/cash situation- points are in two different categories. They switch from DVC points to reservation points and can't go back. So you have to be sure you won't want to change plans.
The value scale tips with the food and entertainment included on board when you only have 3 traveling. Hotel Room points are cheaper for a larger family.
For us- we realized that the magic of the ship still holds a lot of awe for our dd10 who will turn 11 on the cruise. It will be her last chance at the younger clubs.
At 10 she is also now a full price ticket in the parks, but does not yet like the E ticket rides. The rides will still be there in a year or two.
We ended up with about 3 years points to spend now because of weddings and graduations in the works with extended family will prevent our using any next year for our usual family trip. Cost of airfare prevents us doing multiple trips.
So we stretched our points out by choosing the cheaper point cruise, (Yes, some dates are less points than others),the smaller studio hotel rooms before and after for a few days knowing we will be at the parks so we really do not want to cook that much this time.
If I were to do it again- I would book the vacation in the parks precruise. Then the cruise and definitely not over the holidays for the return flight.
It's a learning curve.