I have looked at the SIG program as we are quite close to the campus you are (likely) considering. I thought that the courses did not look very rigorous - and my kids are MG/HG types. Of course, it would be best to hear from someone who attended. Also, SIG costs quite a bit.
There are other programs in the area, though I haven't researched all of them. My kids never seemed too keen on going to school in the summer and a lot of summer programs conflict with travel softball. My middle kid (had just completed 8th grade) went to a creative writing course last summer through Pennsylvania Writing and Literature Project. Her teacher was the gifted coordinator in a highly regarded local middle school. My kiddo enjoyed it and it wasn't expensive. Go to
http://www.pawlp.org/ and go to Youth Programs and look at the 2013 brochure. Might look at some summer sessions at local private schools too - some courses are academic, but others look fun.
