Graduate school holding a diversity committee meeting. What do I need to do to be effective?
We (and indeed you) clearly cannot read the minds of those who have called the meeting, however I'd like to suggest a third option:

Someone in the administration is definitely trying to do something, but because universities are large and cumbersome organizations, change takes time.

The best things you can do are heading to that meeting prepared (which you appear to have done) and with an open mind. Assume the intent is to have a productive meeting, but also one that likely won't have a great deal of actionable things come out of it. First meetings rarely do. Express that you've got ideas, and are willing to work with them. And find out who the people are who you should be talking to - if the meeting does seem like it's sincere, try to finish by identifying at the very least who you should talk to about "next steps".

In terms of leverage? Almost none. But that doesn't mean you can't get things done - university administrators are human beings, and they too care about things. For example, at my university, the problems of first generation students are taken quite seriously and we still struggle at times.