My recollection of visiting in the 1960's and early 70's is that the shows were free. You had to tip the maître d' to get a decent seat but there were no tickets required. I remember seeing Sinatra at the Sands once when I didn't know the protocol. I walked up the door and said "I'd like a table". The maître d' pointed to a little table with one chair next to his station and said "You can sit there if you want". And I did [g]. Great show, but Frank was a loooong way off. It does seem to me you were expected to buy at least one drink, but that was it.

Wonder what year the hotels decided to start selling tickets to the shows. Seems to me it's about the time the price of meals in Las Vegas was upped to make a profit, not just lure people to the hotel.