The Tzaar Baalei chaim question is an interesting one and I cannot comment on that. That is something to ask you Rav. However… as mentioned… tznius is a huge issue on 2 fronts. The performers are far from appropriately attired… and the general venue is typically not a tznius setup. You have mixed and close seating, facilities, lines and entrances… and you have the way many people dress to such events. While you may not have a choice in the general street… here besides the choice of not attending… you are in a tiered stadium setup with them all around you. It is very rare… but they do actually have frum circuses once or twice a year. There are videos of them as well.