So, 'just music' is powerful. Very powerful.
That said, once you've got a station up and running, you've now created an incredible platform for any kind of 'message' you want to put out there. Be it music that people don't normally hear, local musicians that don't normally get any kind of airtime, commentary on a broad range of subjects or news that's not mainstream.
A pirate radio stations got to use it's resources as well as it possibly can. Each station's going to be different, but I personally think that each group should designate a small sub group that's dedicated to creating local news that's specific to the community. A group that searches out issues that mean something to the people that live in that town or area. They should also work at creating a place for people with different (and not always popular views) to get those views out into the collective community discussion.
This may seem obvious, but it's not as easy as it sounds. It takes time and effort, and dedicated folks that do it day in and day out. You've got to find people that are dedicated to the IDEA of creating this alternative platform for news and commentary. Again, each station will be different- some will have a specific political view and leaning and will only create a platform for that point of view. I like the idea of creating a media outlet that's open to anyone who really wants to use it. This creates a promise of controversy, and can be hard to manage, but it's something that doesn't exist in today media world and it's something that's sorely needed.