Personally, I'm in the MCAT Advanced class as a retaker and I think the coruse is worth it and wish I had done it the first time. The amount of resources you get and the instruction makes it unmatched. For the advanced section, the instructors are required to have scored somewhere in the 95 percentile I believe.. or at least both of my instructors have scored 35+. I've already received several test taking tips I never thought of and that aren't even part of the Kaplan method that I'm sure will help me A LOT when it comes time for test day.
All that being said, I get 50% off my course because of my affiliation with a pre-med organization and they also have a promotion going for a $200 rebate off of your course.. so I'm only in the end paying $800. Still expensive, but I don't want to retake again so it's worth it IMO to just get it over and done with and with a respectable score nonetheless. If I didnn't have these discounts though I likely would have thought about making that type of monetary commitment a lot more before making a final decision.
I think, having used EK to prep the first time, with free time like I'll have this summer I think I would have had no problem pulling off a 30-32. I honestly feel that already with the style of teaching for my class, and the practice I'm getting, that I can realistically aim for a 35+ without a problem.
The books are the same as for the regular class but I can't comment on the quality of the instructors or the lack of extra materials that are supplied for my section. Thumbs up from me. If you've always been a self studier, there are plenty of resources out there which will help you on your way without paying for a prep course. If money isn't an issue, why not.