If you are looking for statistics, I think the class of 2016 was 33% AIMsters. This year, Objee posted 15 LOAs were given out to those that attended AIM. As for experience, my DD attended 4 summer seminars this past summer (USMA, USNA, USAFA, and USCGA) and said AIM was the hardest. Unlike the other Academies which had one or two days of "Beast" with a few days of classes or activities, AIM is a week of Swab Summer. DD loved her experience and was able to make friends with others who had a desire to attend USCGA. AIMsters are also reviewed by their cadre and those reviews go into their admission files, so it's a chance to make an impression. The week of AIM allowed DD to gain contacts with current cadets she could ask questions of, and also future cadets she could be friends with. It was a great experience for her, especially now that she has received a full appointment for the class of 2017!
If you really want a nuts and bolts answer, you should PM Objee or Luigi. They are the ones that know.