I think we're going the same direction. The investment is less before you have to change. If you spend 6 months gathering requirements that are obsolete (or wrong for unanticipated reasons) before they're finished, you've lost 6 months. Working in an iterative process ("Is this what you want?", "No, how about this?", "Or this?") reflects the reality that requirements change sometimes for external reasons, and sometimes because people don't know what you want.

Agile also shouldn't be an excuse not to document. My (perhaps not fully informed) view is that it's more about iteration.