I only find those reactions appropriate if they were a HUGE fan of the departed, ie. X was their #1 favorite celebrity, X's work helped them get through a difficult point in their life, etc. If they just casually listened/watched/whatever and they make a big deal out of the death, it feels like they're just following everyone else.

I liked Bowie's music, but he wasn't my favorite artist. When I heard the news, I was saddened, but my thoughts instantly went to a friend of mine who was a huge fan (his music was inspired by Bowie's style, for one). He understandably took Bowie's death very hard, but for me to have that same reaction would have been inappropriate.