greenmonster,
Many of these schools attend other showcases as well including Stanford camps, PG WWBA in East Cobb and AZ.. If you have the grades and ability to play at most of these schools I would go. Especially if you have had started a dialogue with some of the coaches and they have shown some interest. If you have a tough time getting to the school specific camps this may be the best way to thin out the herd to find out who is truly interested.
My son went to HeadFirst in 2009 and all of these GPA schools were there at that time plus many, many others. GPA started last summer. He currently plays for one of the GPA schools. This appears to be a much more intimate setting (than HeadFirst) with just 7-8 D1 schools and Trinity but I would want to find out how many players come to these camps. If my son were being recruited again, we would probably be going to this. I think it is more than fair to ask coaches specific questions about this showcase. Example: How many has he recruited from this event? Has it been a success and why? Also, you may want to contact the GPA folks directly to find out how many kids attend these camps. That is the biggest question in my mind. Is the coach to player ratio manageable & personable or do you feel like herded cattle? Please let me know if you find out. Thanks.