The first choice for an evening in Jiuzhaigou is the exotic dancing and singing performances of the local Tibetan and Qiang people. Ethnic groups in China are well known for being good singers and dancers, expressing various emotions of daily life.
The Jiuzhai Paradise Theater 
located in the Jarpo Town Hotel organizes a wonderful performance every night. Actors and actresses wearing colorful Tibetan and Qiang national costumes perform songs and powerful dances to express their beauty and bravery. Audiences are invited to participate in the Tibetan Guozhuang dance, usually held during important festivals or events. People sing and dance in a circle, changing their movement according to the musical rhythm.
Most come to Jiuzhaigou for it natural splendor and the traditional culture of the Tibetan "nine villages," and pretty much everything you'll find here returns to those themes, whether it be ethnic performances in plush hotels or the small stockaded villages within the park. Of course, much of what you'll see has been consciously produced for Chinese and foreign tourists, sometimes creating more of a theme-park feeling than a sense of authentic experience.
That said, Jiuzhaigou and its villages are undeniably beautiful, and a day out in the fresh mountain air sends most back to their hotels eager for nothing more than a good meal and a good night's sleep, with little concern for the "authenticity" of the day's experience.
If you're looking for something beyond the usual, annual festivals and temple fairs are a good time to be in the area. The following two fairs are particularly good ones to hit for a more spontaneous sense of the region's traditional people and their culture.
The Liangmin Wangqing Temple Fair takes place every January 5th, according to the Chinese lunar calendar, which means it can take place any time between early January and mid-February, so check to confirm the actual dates if you're interested. A commemoration of the death of a famous Bon Lama (Bon being the indigenous Tibetan faith that predates Buddhism's arrival), it is a period of intense religious expression. Lamas and monks chant as Tibetans from all over the region come in traditional garb to worship.
A more festive event, the Mazi Fair (usually held in early May) is a grand religious festival held at Zharu Temple. After abstaining from eating meat, chanting and rehearsing for days, lamas and monks lead this springtime celebration as laypeople from surrounding communities enjoy Khatag and Tibetan opera, song and dance. The festivities spread into the surrounding woods, as celebrants stroll, chat, drink and sing the fair away.