The Wildrose Alliance is talking about giving a tax break for volunteering. I can't see that is anything close to a good idea. It runs contrary to the human motives about wanting to contribute to the greater good. Volunteering is not about individual rewards but participating in something greater than yourself.
Daniel Pink talks about the motivators of Autonomy, Mastery and Purpose for volunteering. People do what they love because the love it and payment - like tax credits sullies the sense of contribution. Community is formed by intrinsic rewards being enough of a motivator. You don't strengthen a community by paying people to do what they love. Remove barriers and increase capacity for people but don't insult them with payment to do what they love to do.
Listen to this video on the research that shows why this is.
The attitude that you can put a cost on everything tends to be blind to the fact that what people really value.