Did you know Mathematics SE’s birthday graduation was on October 25th? Congratulations!
I don't know if this community would be interested in something like this, but how about a contest or some other fun activity to stir things up a little? After a year of great Q&A, we'd like the opportunity to "give back" for everyone's hard work.
Anniversary events are a great way to spark some interest in the extracurricular activity in your site (more meta participation). An “anniversary event" can be just about anything. Take a look at Super User’s 2nd Birthday Super Contest for inspiration. It doesn’t have to be a contest. Dream up whatever you feel the community will find interesting, and go for it.
Start a meta post or chat event to work out the details. Rally support for your event and bring it to our attention (email@example.com). We're really interested in community-led initiatives, so let’s just say, if you can work out the details, we’re very motivated to say “go for it!”