I don't know what to think about this issue.. There is a huge demand for recreational parks, I just don't know if it'd be recognized on the large scale in the private sector as is done under the NPS. I struggle with this issue as a Libertarian.
I would prefer a system of trusts. If that fails, I am not going to complain about national parks though. If you have ever been in these wild places and felt like you were the first person to ever see it, pretty powerful experience. Selfish? Damn right but it's something I enjoy as well as many.
The US isn't Europe and we haven't fricked up our wild spaces yet. There is value in preservation. Again, I would prefer a system of trusts, but figure you can meander your way enough around the constitution to justify it (like anything) if you choose.