Here's an exercise that I've found helps people think about vision: "Cast yourself forward three years (or whatever your planning horizon). Imagine you are sitting at home, reading an article about our company three years from today. The article talks about the remarkable success our organization has achieved. Imagine the headline and the story that accompanies the headline.
"Write down the headline and the story in your own words. In the story, describe what were the most important decisions that propelled the company to this success. Who made them? What specific things did the company do? Talk about what conflicts it had to resolve along the way."
When people are ready, ask them to share their headlines and stories. Then ask people to share their emotional reactions: "Which stories excite you?" Second, ask them to think analytically: "What are the rationales for each vision? What's the value to our customers? What's the benefit to the company?" Keep asking those questions and eliciting responses until people gravitate toward a well-defined vision.