If you are interested in that approach, here's a couple of tips. First, try to show users something as soon as possible. In an ideal world they arrive at your page and immediately see a graph that tells them something interesting about themselves or something they relate too. Typically this isn't achievable, but at the very least have a single step where they enter an email address, twitter name, etc and then within a few seconds get some information. You should also show an example of what they will get on the landing page. These techniques reduced my bounce rate massively, never overestimate people's patience, you constantly need to be convincing them to spend time navigating your site.
The second key is presenting your statistics in an actionable way. If you can not only tell a user something interesting, but cause them to do something based on that information, then your chances of a repeat visit shoot way up. Feedburner has an 'Optimize' tab that guides you through ways of increasing your traffic. I found that changing from just showing your most-frequently-contacted friends to sending a report of the people you used to talk to and haven't for a while ('Losing touch report') and giving them a link to email each person alongside the list turned it from an 'oh, that's nice' to a must-have.
This is smart.
Your data strategy must a.) provide value to the user immediately. b.) data and visualizations in an actionable way.
In an advocacy context, I would suggest that good data visualizations create a common focus point (inspire discussion), set a common language (visually based on what data you display) and give them options to engage each other because of common or opposing understandings of the data.