I think it really boils down to knowing your audience. An advanced participant will definitely benefit more from a collaborative learning environment. For them, it's more about developing lasting relationships, networking and building upon ideas.
But if some of your attendees are novice to intermediate, they're likely to be more like sponges. They want to know the tools and tricks to success. The more they walk away with, the more they feel like they got their moneys worth. They often learn best from case studies and lessons learned by experts. They're also usually less comfortable joining in the dialogue. Technology can help the collaboration of these learners by allowing anonymous questions or online forums before or after the event.
What I find that really makes a difference in promoting future attendance and loyalty is finding a way to touch not just their brain, but their heart. If you can make attendees laugh or cry, you're session/conference will be more remembered and shared beyond the 4 walls.