At the risk of belaboring the obvious, if you go to a theme park, of course it will be planned rather than spontaneous. While you may be able to find less touristy settings with some effort, the mere fact of your presence as a relatively wealthy foreigner is going to mean that what you observe is different from spontaneous interaction inside the minority group.

Minority culture as it exists now has been affected not only by recent capitalist commodification, but by the earlier Stalinist policies of defining and recognizing minority nationalities and folk culture and encouraging low-level education in the ethnic language, and even providing some privileges such as exemption from population control limits, while discouraging development of separate modern cultures and separatism from modern Chinese society. The minority groups might not even exist in the same sense otherwise - the largest minority group in China is the Zhuang, who were only distinguished in the '50s when their home language was classified as in the Tai family instead of Sino-Tibetan, and enrolled as a national minority over their protests that they were simply majority Han Chinese. Further back, the minorities have been within or at least interacted with the Chinese system for millenia, and their cultures are products of that interaction and not isolated developments. For example, the legendary king Chi You was a bad guy defeated by the founding Yellow Emperor nearly 5000 years ago in Han Chinese mythology, but is revered by the Miao/Hmong as their ancestor.

Your reactions can involve not just the minority cultures per se and Chinese tourism culture, but also Western ideas about tourism, minorities, and nature that you may bring to the encounter. Northern European Romanticism in particular likes to idealize nature as untouched by human presence, and ethnic people as noble savages free from the corruption of modern commercial life; the most satisfying experience is to encounter the most untouched landscapes and people. In contrast, Chinese tourism sees a striking rock formation as all the more beautiful and interesting when scholars of past dynasties have chiseled their poetic commentary on the rock, and sees a shiny new reconstruction of a historic structure as an improvement over a faded and damaged original. It is not surprising that Chinese attitudes towards ethnic tourism also value activity and interaction rather than aloof authenticity.

"Can you think of another function that cultural representation from the inside fulfills" Wow, that's an interesting question given your discription of your study. The first thing that pops to mind is "Is it exploitation if those that are presenting themselves are the subject of what would be exploitative if done by others outside of the minority?"

For me, an example would be the Wild Bill shows where Native Americans were presented in a certain image by Wild Bill. That was exploitation. Now, imagine the situation that you are experiencing where there is no "Wild Bill", but only the ethnic minorities presenting their own culture from their own (consumeristic) perspective. Are they exploiting their own heritage?

Not sure if that helps, but that's what jumps into my head.