Whether it is worth the points or not is a widely varied opinion. One opinion that is not varied is that you should not buy points if your sole intention is to cruise.
We have cruised on points before and paid cash for cruises. Both time I felt I got my moneys worth. (I have also rented points.) Depending on what time of year you cruise, your calculated "exchange rate" will vary. In the fall,
DCL offers alot of discounts on the cruises, so the point exchange is rather low. In the summer, it is higher.
Another factor people disagree on is the value of the points. I usually compare mine to what I paid for them. Others value them at what they can rent them for. Paying with points has little risk involved. The biggest being you need to cancel your cruise and thus your points become reservation points. If you rent out your points you have all the risk of renting. The buyer doesn't pay up. The buyer decides to cancel his trip and wants his money back. etc.(all these issues need to be settled before you rent)
The rules for booking a cruise are that you can book as early as 11 month out. Once you book the cruise, the points belong to
DVC. If you cancel, you will only be able to use those points in the Disney Collection or the Conceirge Collection. You can book using a combination of cash and points. Each person has to be booked with either points or cash. A single person can not be booked with part points and part cash. All cash (plus a $75 exchange fee) are due at booking. No deposits with balance dues at 60 days. This rule is why we usually book cash. Not that we don't think it is a good value.