I only have a book that has the 2008 points for DCL, but a September cruise, Category 9, for 4 people would run anywhere from 250 to 330 points. For 2008, it was 111 for the 1st two people, and ranges from 18 to 61 points for the 3rd and 4th person (depending on the age of the travelers).
I do think that the value of the cruise is more than the value of the DP's, but not everyone can take advantage of the cruise dates, and therefore, not necessarily the better deal unless you can.
I am a teacher and all the sailings were during the school year so I had no option but to take the DP's.