Myself (27) and boyfriend (29) love the campfire and movie. We make sure to go at least once or twice while camping, just depends on which movies they will be showing. If you don't want to stay and watch the movie, stop by and roast some marshmallows, it really is alot of fun. The first time we went, we saw Tarzan - very cool to sit under the stars with some snacks and watch that movie!
I know you will not feel out of place - at WDW adults are just big kids so do whatever makes you happy!