The Nobel Prize is not very important for the winners - they are usually pretty successful people already. But it is valuable as a way of drawing the public's attention to important work in economics.
If budget planning requires gathering information from people who may not always have the incentive to disclose that information, then the principles of mechanism design can definitely be of use in such planning.
A properly designed tax system can strike a balance between helping the poor and, at the same time, giving people the incentive to work.