Damn, mbw..... That's a lot of salt! Luckily I don't have to worry about that here, but back in MA where my family lives, they salt the roads like crazy. It's good you hose it down, as the salt is so corrosive. You are right, nothing wrong with dirt and mud - though, I do try to wash it away from various areas.
I'll let you know how my undercarriage steam cleaning goes tomorrow, which will likely be a one time thing to start with a clean area so I can install my skids. Going forward, I'll likely just pressure wash it myself like I usually do - works pretty well.