I have launched a few national grassroots campaigns, and have seen the tremendous growth in the quality and complexity of products that are out there. I stay on top of the new technologies to best advice clients that looking to add a grassroots piece to their current or future advocacy efforts.
I agree with Dan, except that I think it depends on two factors, first - what your app is going to cost, and second - how much is going to cost you to acquire paying customers once you have an app.
You might want to consider getting advice from people working in or around your target space to get some better perspective. POPVOX and Votility have great leadership that might be willing talk to you if you aren't direct competitors.
If you are in DC, 1776 has a great educational events and staff from the start-up community that would probably be willing to talk to you as well.
I am happy to follow-up on any or all of this. Good luck!