I appreciate your opinion, since Bill's reading them. Back when they first came out, I knew some young people who were over-involved, buying all the accessories, making costumes, etc. We discourage our children from excessive enthusiasm over any fiction.
When fiction begins to be problematic, imo, is when you want it to be real.
Heh... nothing wrong with dressing up for special events. Just means the kids might be a little on the geeky side.
I've often been excessively enthusiastic about fiction, but I've read so much I don't dwell on any one series. I think that minimizes any harm.