Are Satisfied Volunteers Motivated to Make the Most Contributions?

One of the things that our organization has struggled with for a very long time is turning volunteers into donors. Our organization relies on the support of many episodic and event based volunteers, the "one-off" volunteer is quite popular with our organization. However, we do have a large base of individuals who contribute their time and talents on a regular basis. Some of these are members of our organizations, some are not. But turning those that are members into larger donors is a challenge. We always struggle with how much is too much to ask? We ask their time and resources, how much more do we ask for. I work with a lot of groups that struggle with the same question. How much is too much to ask of your volunteers? Those that are involved at a higher level of volunteering - board, committee, etc. - do tend to have higher levels of giving. I always look at this issue as being the intrinsic and extrinsic reasons for volunteering. Typically in organizations I've worked with, those who volunteer because it's the thing to do, or to be part of the group, actually tend to give more funds to the organization. At some of the groups I work with, we always question if it's because it's easier to give $ than time for these people.