Just some random thoughts, which may or may not seem relevant:
I don't think the Idaho DOA letter is all that bad. It's certainly not a "cease and desist" letter, and it's not enforceable. It's just asking for cooperation. That being said, I don't think one agency has any business "pimping" for another agency--in this case a state agency doing it for a federal agency. Each should speak for itself. But in the interest of inter-agency cooperation, I can imagine a discussion over lunch where one agency rep who might have a little more influence in an area might say to the other agency's rep, "Oh, I can write a letter, and maybe that will solve the issue." No big deal.
On being confrontational with LEOs, I think that's a real mistake. None of us is smart enough (including the LEOs) to know all of the applicable laws and regulations. In my previous life as an attorney for almost 47 years, in addition to private practice, I had some subset positions--as a JAG in the USAF, a Municipal Judge, and a Justice of the Peace, and I can tell you that it was impossible for me to "know" all that I should have known. But if a LEO is going to threaten some sort of prosecution, s/he better be certain that there actually is a law or regulation that applies. That's a basic. That's why many LEOs carry a pamphlet with a synopsis of the laws and regulations that they most often have to enforce, and that pamphlet was prepared by someone else. So getting miffed at that LEO that something was left out isn't the way to do it--but pointing out the missing language is appropriate, just not confrontationally. You're trying to avoid going to court, not guaranteeing that you will go to court.
A simple example: When I was still in practice, I parked downtown and got lots of overtime parking tickets. But in nice weather, I rode my Vespa, and I purposely parked it in a doorway alcove of the building where my office was--on private property, expecting I had ameliorated my ticket problem--and I had permission from building management to park there. But I received a ticket from the City Parking Enforcement for parking a "motor vehicle on a public sidewalk". My solution: first I called Parking Enforcement and asked why they thought it was illegal to park there, and was told that the sidewalk goes to the building. The person I talked to wasn't willing to acknowledge that the building's owner owned that part of the sidewalk, not the City. So rather than going into a tizzy, I sent a nice informative letter to the City Attorney's office, asking them to advise Parking Enforcement that they had no authority upon private property, and that the alcove was indeed private property. A week later, I received a call from an assistant City Attorney, agreeing with me, which he followed up with a letter copied to the Chief Parking Enforcement officer. Nobody got angry, nobody felt belittled, but the job got done--they were wrong but didn't know it.
Another example, closer to the issue being discussed here. When I went turkey hunting, I shot at a specific turkey--and got him good. But a stray pellet got another turkey a good 8' from the first one, and killed him dead, too. I suppose I could have buried one of them and just kept the other, but I brought both of them back to my pickup, in the garbage sack I had with me for that purpose. As I arrived at the truck, a Wyoming G&F officer walked up and asked, "How's the hunting?" I was really upset with shooting two accidentally, and I told him so, and that I really didn't know what to do about it. He said that he saw what had happened (good thing I didn't bury one!), but he had to make a record of it, so he gave me a warning ticket. No harm, no foul (well, some fowl

), and my contrite, apologetic attitude played a part, I think, in not getting a "real" ticket.
Suing any agency, whether of the State or of the Federal Government, is a very expensive, time consuming process. The feds have the Federal Tort Claims Act under which most lawsuits must be filed, and most states have a variation of something similar. You can't just sue because you're upset--you have to have a legal basis, and it has to fall within the confines of the applicable Claims Act. Don't even think of doing that, unless the circumstances are really aggravated--and nothing I've seen in this thread sounds very aggravated to me, FWIW.
On whether other agencies than the FAA have any authority to govern some aviation activities, in fact they do. The NPS and NFS certainly have the right to close or open airstrips on the public lands that they administer, and as Mike V said, many have their own sub-regulations in the form of land use plans. The CFRs may not have a specific prohibition, but that's not the whole story. There are also interagency cooperation agreements, and a whole host of various ways that one can find himself in difficulty with this or that agency.
Lastly, I have to say that I'm a little disappointed at the tone of some of the posts, not that anyone shouldn't have the right to stand up for themselves, but the
ad hominem way some of it was done isn't good. It's Zane's right to do or not do anything about it, and from my observation he's always tended toward letting us self-moderate up to a point. But to avoid heavy handed moderation, I'd like to suggest that this forum is one of the more gentle aviation forums on the Internet, and I would hope that it will stay that way. We can agree to disagree with one another without calling each other names or impugning each other's heritage.
Cary