Recreate the bridal bouquet and groom's boutineer (sp?). I did this for my MIL & FIL's 50th anniversary, and it was a huge hit! I took a wedding photo to a local florist who could tell what the flowers were, and then he did an amazing job of recreating them. I brought it to the restaurant, and then surprised my inlaws with them. We took pics of them standing together, like newlyweds. It was very, very sweet. I hope to double frame the photo of their 50th with their wedding photo someday.
Also, I took their wedding pic and had it put on a cake at Fred Meyers, and I had them recreate some of the details of their wedding cake. It was mildly cheesy, but they loved it!
My MIL & FIL are not extroverted people, so they told us they did NOT want an open house. So, I'd ask first before doing that.
Good luck! And congrats to your folks!