I don't think you can compare test preps to essay writing services. I had a friend that used essayedge and he said it was a total waste of money. I wouldn't put the money into it if I can just get suggestions for free from peers, english professors, and people on this site.
As per getting ideas, just look through those books that you can get from barne's and nobles about writing good essays or at accepted.com just as a way to get ideas of what to write about.
Now why I say there is no comparison between test preps and essay writing services. Essay writing services sometimes write your whole essay for you which is like someone taking a test for you.
Test preps just teach you the material and give you practice materials to help you prepare for the test and to give you a good starting point of where to begin the review. Also, test prep materials can be obtained without taking the course through students selling their materials for a much reduced price or peers who let you borrow their stuff when they are done with it.
Just because one takes a test prep doesn't mean they'll get a score like the one you got, Justbreathe. It just means that they will have materials that help them better prepare for the test. And taking a course doesn't guarantee a better score then someone who didn't take a course. In fact, if you pay the money and don't do anything but attend class, you probably won't do as well as someone who utilized all the resources that they paid the 1500 dollars for.