From my own experience, I felt that taking a course would be unnecessary since there is only so much the course will do; you have to discipline yourself and study on your own anyway so might as well save that money and put it towards more test prep material. I just read several breakdowns on the DAT Discussion section of this forum and figured out what I wanted to buy and what studying strategies would work for me. There is really so much valuable information on SDN that can seriously save you a lot of cash!
I wouldn't bother getting CDP, I only used the 5 DAT bootcamp tests for PAT the week before my test and scored a 21 in perceptual ability. I also thought that Chad's videos along with the destroyer were more than enough for gchem and ochem, especially for the price.