We went for our 20th anniversary last year. We mentioned it when booking our reservations, and when we checked in. The CM handed us anniversary badges and that's about it. I had heard so many stories about how the front desk would send surprises to your room for anniversaries, but we didn't get anything. We wore our badges to the parks and restaurants, and we got a few Happy Anniversary wishes from people, but that's about it. So the next day we decided not to wear them and left them on the nightstand. When we got back to our room, there was a stuffed Stitch on our bed holding balloons. I was so surprised. Then the mousekeeper came to the room and said "Oh you're back, I had a card to add to your surprise. I was cleaning your room and saw the anniversary badges on the nightstand and wanted to leave you a surprise." Well, it was just about the nicest thing anyone has ever done for us at WDW! I almost cried. I bought her a card at the gift shop to thank her, and I also wrote the manager of the WL and told him what a great employee she was, and how much we appreciated it. Never heard back from the WL though, but I hope they know what a great CM she is!
So I tell everyone not to go expecting anything, but if you do get some little recognition, just enjoy the magic!