I also participated a dental summer enrichment program at Marquette back in the summer of 2001. This is one I got out of it:
1) stipends
2) friendships - the people I met at Marquette that summer, I'm still in touch with them today (we're all dental students now)
3) exposure to dental courses, materials, and instrutments - this really helped me to be ahead of a lot of my classmates when we started on day one as far as dental lingual, techniques, and knowledge
4) exposure to all dental specialties
5) an application booster
If you have the opportunity to be involved in one, do it! I strongly recommend it!