Yes, the world would be a happier place if people dressed up in ape costumes, because ape costumes are funny and they convince people not to take life too seriously. Ape costumes make people smile. Especially if a person can walk on their hands in an ape costume. That is just amazing.
More people dressing up as apes would not increase the happiness of the world in any real noticeable way. It might make things slightly more whimsical and entertaining but in the end it would not have any serious impact on the basic conditions of life and therefore not make the world happier.
Although some people may find happiness in dressing up as an ape, I don't think the majority feel this way. If you lived on the equator, for example, it would not be a pleasant experience. Equally if you were in the South Pole, would an ape costume really be suitable clothing? I think the majority find happiness in other ways.
Not being able to see a persons face makes me feel incredibly uncomfortable. While costumed escapades might bring joy to some people, I find it hard to believe that I'm in a minority in my feelings. Disney World is my worst nightmare, I wouldn't want that experience in my everyday life!