So first, maybe I should describe more about how I did my application, and then I'll answer specific questions.
I applied to the NSF GRFP in November 2009, the same time I was applying to graduate programs. I was doing research as an undergrad, so I worked with my adviser at the time on my research proposal. The research proposal was an extension of what I was doing at the time. So it was original, but it was a logical extension of our work, so it wasn't too original. Below are the intellectual merit criteria and you can see that they focus on new research that is doable.
Intellectual Merit
- How important is the proposed activity to advancing knowledge and understanding within its own field or across different fields?
- How well qualified is the proposer (individual or team) to conduct the project? (If appropriate, the reviewer will comment on the quality of prior work.)
- To what extent does the proposed activity suggest and explore creative, original, or potentially transformative concepts?
- How well conceived and organized is the proposed activity?
- Is there sufficient access to resources?
Broader impacts is more difficult to address. But here are the actual criteria.
- Broader Impacts* – Activities and projects that:
- How well does the activity advance discovery and understanding while promoting teaching, training, and learning?
- How well does the proposed activity broaden the participation of underrepresented groups (e.g., gender, ethnicity, disability, geographic, etc.)?
- To what extent will it enhance the infrastructure for research and education, such as facilities, instrumentation, networks, and partnerships?
- Will the results be disseminated broadly to enhance scientific and technological understanding?
- What may be the benefits of the proposed activity to society?
So it is an advantage if you have done some teaching / tutoring previously, but it is not a requirement. The last three criteria can all be satisfied by research that recognizes its own place in society, meaning, that one can explain that this research will have a broader impact outside of this one project.
Here is roughly how I think I devoted my essays towards each criteria:
Personal Statement: Intellectual Merit 50%, Broader Impacts 50%
Previous Research: Intellectual Merit 90%, Broader Impacts 10%
Research Proposal: Intellectual Merit 75%, Broader Impacts 25%
So for me, it was definitely tougher to spend a lot of time addressing Broader Impacts, but it is important to address it, even if only a little, in every essay.
I should note that since getting the NSF GRFP I have changed research interests twice (still within physics) and that has been no issue. As others have put very well, the NSF GRFP funds a person, not a research proposal.