1) apply lessons from social networks, and 2) define standards for .com/petitions sites
Let's agree that a communication requiring .gov to respond has inherent value e.g. https://wwws.whitehouse.gov/petitions. The bad news is that unless this site catches on it will disappear in 1 to 5 years along with its value as the Internet voice of the 99% and 1% alike.
Minimally, 2 things are needed to enlarge user base and develop site loyalty so users become advocates for preserving this value.
1) People are at their best when they interact and collaborate. So, take a cue from social nets and encourage people to collaborate on every aspect of developing petition... from initial vague idea to submitting petition. This will help improve petition quality and focus. Also each interaction is an object lesson in civil discourse (something most of us could benefit from)
2) Government should not own or manage .gov/petitions sites. Rather, it should define operational and civil discourse standards in a way that stimulates .coms and .orgs to innovate their own .../petitions sites. Government agrees to "listen" to sites that comply with standards.
.gov/petitions is a tremendous gift to the American people and one we need to protect.
Think Facebook of political discourse.