Anytime you need to pay 1000 per night + for a normally 150 dollar a night hotel room yeah a return on investment can be very questionable vs. just advertising here or on any other website.
Generally the rooms sound like crap anyway, and even if it sounds good mostly people sit for 5 to 10 minuets, and may or may not remember the experience 2 hours later unless they are seriously looking to purchase a product for a specific purpose, and that is why they are there in the first place.
For sure Attendee's can benefit just like any other weekend hobby, but for Exhibitors it is excessively expensive customer acquisition cost. Hence most of the 20 huge names in audio can benefit just because everybody knows who they are in the first place so they of course like this as they get their costs supplemented by all the garage engineers renting the 100 other rooms keeping their costs down.
98% will always be tire kickers at these things, or looking for really low price show demo's at best. The 2% interested in even that will be spread very thin considering now you have 300 to 400 high end vendors all in one hotel for 3 days. Most of the smaller guys try to band together to display in a room or several rooms and offset costs. Whether this actually works probably depends on the way the wind blows that day.
Then again the Big guys generally band together as well in some cases and take most of the share in the end.
It could be argued the show management, hotel, and some of the dealers are the only ones that really make out on these things. Likely not so much the manufacturers themselves. Which many times you just see the local dealers, or regional distributors exhibiting on behalf of the manufacturers anyway, and the manufacturer might send a rep on a flight to be around, but at minimal cost.