If you have a high pressure tank in your passenger compartment you should remove the regulator when you're not using it. If something were to hit it and break it off the tank, you wouldn't want to be in the vehicle with it. Though I don't recommend just having it loose in a tool box.
I know it's an ancient thread, but yes, regulators will "wear out". Mainly the diaphragm will weaken. But seals can eventually leak also.
If you're interested there's a shop I know of over in Snellville that rebuilds regulators. I've spoken to them on the phone and they seem to know their stuff.