Ok, full disclosure: I never used a prop, so I don't really know if they're effective.
However, I would only bring a prop if you think it really adds to your discussion, or clarifies something that might make you easier to understand. For instance, a guy in my CSL class was talking about the erhu, a Chinese stringed instrument, for his DS. He brought in a diagram to help him indicate which parts of the instrument he was talking about, which was relevant to the instrument's structure and function etc.
With the hikikomori example, I think bringing in a photo of their rooms (for instance) would actually detract from your presentation - surely you could use a 四字熟語 or something to describe the situation more vividly than a photo could.
I will say though, props could probably serve as very handy memory aids, because they're so concrete. If you do find yourself forgetting stuff, might be a good idea.