Personally, I see them as an opportunity to meet manufacturers or their representatives, who are rather difficult to contact the rest of the time.
It's a great way of networking, meeting people and negotiating things with hardware suppliers, or at least making contact with them.
Who visits them?
Professionals in the sector (manufacturers, miners, developers, traders) and also people who want to listen to well-known personalities in the field on very specific subjects.
I think the best thing for you, OP, would be to go to a few events and you'll be able to make up your own mind about them and their audiences very easily.
Sorry, I don't want to click on that docs.google link, so I replied here.