In response to joe bartels' reply:
Joe, I think you've described the problem very well, and in so few words. What some people call wilderness is simply an area outside of town. Such areas are frequently visited, sometimes by hundreds of people per weekend. These areas are not true wilderness, and in fact are just a buffer zone through which people who don't want true wilderness won't usually cross. Mr Zimmer also made the same allusion below your comment when he stated that it takes a day's travel to leave the beginners behind.
My point above was that traffic and impact are related. High numbers of people is the cause, and negative impact is the effect. Thus, impact fee = traffic fee. Basically, you are charged a fee because everyone wants to go there. I'll go one step further here. The fees are not to reduce demand, since once an area is highly trafficked the demand continually builds. Once the traffic reaches a critical mass, the demand becomes inelastic, and the fees are not to reduce impact, but to generate revenue. (Side note: Why is the ranger necessary? To keep people from doing things they would be doing in urban areas but shouldn't be.) Because of the occasional public outcry, like the one seen in the AZ Republic on Feb 2, some of the fees go toward impact mitigation, like picking up litter and building more restroom facilities. In this manner, an increasing number of people can be sustained in a small area of wilderness, and demand builds to the point where it is highly inelastic, and fees can then be raised again.
The only way to unconnect the circle (so to speak) is to maintain the integrity of wilderness areas by keeping roads far away from them. Once the asphalt goes down, it is a given that the boundaries (buffer zones) will be trashed. At that point it is inevitable that the fee boxes and restrooms will go up, and most of us believe that the wilderness starts where the large permanent structures stop. I'm in favor of the existing buffer zones, because they divert people who would otherwise create more buffers elsewhere. Also, there should always be a way to avoid charging people who want to travel to low impact (read: low traffic) wilderness areas.
So in answer to your first question, there is no such thing as a high impact wilderness area, since impact (=traffic) spells the end of wilderness and the beginning of civilization. In other words, high impact and wilderness are mutually exclusive. Also, just as our taxes pay for city parks, we can consider the buffer zones between true civilization and true wilderness to be "country parks", both in the sense that they're less urban, and that they're owned by "we the people" and operated by us as well, to the extent that we exercise our democratic oversight. Two city parks in Phoenix that come to mind are Papago and South Mountain. Both are good examples of the aforementioned buffer zones. Neither has an entrance fee. And like the country parks, the areas most enforced are the same areas where the most people congregate. The closer I get to a road, the more likely I am to see a ranger. This is also true in the Forests.
You'll also notice in city parks that the fees that are charged are not to pay for impact (which is already subsidized) but to keep demand down. If the soccer fields were free, everyone would use them. Since demand for soccer fields is elastic, fees are highly discouraging, and they effectively allocate scarce resources. On the trails, demand would be allocated by forming a line, but even the suburban trails haven't gotten that busy yet. The only way fees could possibly be justified in forests is if it were proved that each car does $4 in negative impact as it parks at the trailhead, and the forests must necessarily be closed if the fees were not charged. Don't laugh; this happens during extreme fire season, when hikers end up all over tinderbox buffer zones, and the average cost per stupid hiker is more than anyone could possibly be willing to pay. In this special case, the forest could not continue on as usual, with or without fees, and the only rational option is to close the forest to all. However, in most cases, the forest goes on as usual, and suburban projects like Annual River Cleanup Day help to make fees a dead issue.
As it stands now, we have both wilderness and pseudo-wilderness for anyone who desires. The fees are a drop in the bucket, except for the individual user. Let me add here that being the poor person that I am, I bought the backpack on my profile photo fifteen years ago for ten dollars. I have not bought a new camping backpack since that time. So yes, I am cheap, unlike all those hunters whose collective demand to bag an animal is highly inelastic. (Don't believe me?
Check out how much an elk or sheep permit goes for in Arizona! When the cost of going on a hike becomes more than the cost of harassing my US Senator and Representative daily, I will change some of my weekend plans. I hope it never has to come to that, and I'm sure some of the people's servants feel the same way too.