My team has struggled with sustainability this year (not sure if helpful but:
http://www.chiefdelphi.com/forums/sh....php?t=109888), and things have turned out a lot better than we expected. We managed to build a competitive robot despite just barely funding the entry fee.
What we learned this year is that the ideal team structure is not for every team. It turned out that our team was a bit too small to have a full team structure. As such, we began to create a smaller scale structure that has minimal functionality but enables some order rather than none. We identified specific tasks that needed to be done (eg wheel assembly, chassis assembly) and put one of the more responsible students in charge and gave them the responsibility of communicating with all of their group when they were meeting / what they missed at a meeting / taught them how to do the task. These leaders are then kept in check by the adults and team captain. The key thing, at least for my team to realize was that because we don't have a high membership (<10 dedicated members) we cannot pull off the "Programming Team, CAD Team, Design-and-build Team, etc" structure that is classically suggested. Instead, this structure we have while not perfect allows the limited amount of experience to be organized among many different tasks. For example, a recent task for us was bumper construction. A student was put in charge of it and their progress was monitored. When progress stalled, a leader asked what was wrong and suggested possible steps to getting past the problem (or in the case of slacking, gave them a reminder on their position and responsibility)
This is rather specific to my team, and I know your teams situation is quite different, but it might give some insight.