Entrance Fees Going Up

Last fall a handful of parks announced that it'd cost you more to enter their gates this year. Well, the list is getting longer. Here's the latest list of parks I've come across that are hiking their entrance fees beginning May 1:

Death Valley...................from $10 per vehicle to $20
Glacier...........................from $20 per vehicle to $25
Grand Canyon................from $20 per vehicle to $25
Grand Teton...................from $20 per vehicle to $25
Joshua Tree...................from $10 per vehicle to $15
Mount Rainier.................from $10 per vehicle to $15
Olympic..........................from $10 per vehicle to $15
Sequoia/Kings Canyon......from $10 per vehicle to $20
Shenandoah...................from $10 per vehicle to $15
Yellowstone....................from $20 per vehicle to $25

Now here's an interesting dilemma. Currently, parks, I believe, are allowed to keep 80 percent of their entrance fees. With entrance fees going ever higher, it makes the $50 National Parks Pass so much more of a bargain. But if folks opt to buy that pass, and do so either locally, such as through an REI store or through the National Park Service's web portal, individual national parks likely will see a reduction in their fee collections...and thus a drop in operating revenues.
I don't think anyone has run the math on this possibility to ascertain what sort of impact increased fees might have on individual parks. But it's definitely something that should be factored before another round of entrance-fee hikes arrives.