You are correct, NPS side.
Still, the fundamental question remains: do we serve the government, or does the government serve us? Thankfully, that question is answered in the preamble:
We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.
I cannot quite grasp why some defer to language that is meant to be interpreted, rather than followed in rote manner. In other words, we need to look to intent. The '64 act was designed primarily to prevent the kind of development activities being planned like Disney's proposed ski resort.
It was not crafted to prevent common sense, low impact measures to protect both people and nature. To argue otherwise, to hide behind the true meaning of the law, could easily be construed as just a cover for serious social impairments.