charge for access to national parks?

Well, yeah. But if you create barriers to stop people from rorting the system, it also risks creating barriers to stop people who aren't rorting the system but just can't get through the barriers. There are plenty of people struggling with bureaucracies like WINZ right now, effectively because they can't provide the ID and address requirements that it demands. Edit: I'm certainly not meaning to suggest this would be the only barrier, either. I'm just wary of putting up even more of them when I'd much rather the conservation estate were as open and accessible to as many residents as possible.

As Wayno suggested, make hut/access passes photo passes. No further ID requirement.

But it's a new requirement, and that's the problem I described a couple of comments ago. Alternative ideas for raising funds, like a conservation tax, don't have this issue. (They have other problems which have already been discussed, though.)

Interestingly a recent unrelated article described the tourism industry as $11 billion a year. Based on the 1 million tourists a year quoted elsewhere this means they are spending 11k each for a typical 1 month stay. Do we really need to take more money off them or just ensure it gets spent in the right places?

If the 11 billion figure is true, and I have few doubts it is... the tourism industry would be paying billions in tax every year... It must be remembered that the conservation estate is the main reason why people visit NZ, few people go to NZ to visit cities... They come to see the lakes and mountains. DOC currently gets around $462 million dollars in funding, which is probably less then 20% of the current tax take from tourism alone. I personally feel there is plenty of fat left in the government spending, and it just needs to be invested more fairly towards areas which are responsible for generating much of the revenues.