Suggestion:

> At NIL, you can engage as much or as little as you'd like, but we are an organization that survives by the spirited participation of its members.  Try joining a working group, sweeping the floors, or working your way to the board:  don't just *be* here, *create* here.

The original seems a bit redundant, maybe a wee bit verbose.  On the one hand, we're trying to accept any level of commitment.  Maybe your focus is elsewhere, or you aren't ready, or you don't know where to start.  That's okay.  But we can't live without a good cadre of active participant-members.  I think this does a better job of both expanding the scope of "participation" to any possibility and defining that participation as organization-level and not just project-level.  I also like the intentional ambiguity of "*create* here", since it can mean both "create [things] here" and "create [what] here [is]".  I really like the word spirit.  Good choice.