When you write to your representative, that is citizen involvement.  When you pay someone else to write the letter for you, that is "lobbying." It is a false distinction.  Prof. Machan's thesis is unassailable: only Congress and the courts can block regulation.  Citizen's voicing their opinions can only influence the legislators.  Beyond that, lobbying per se is neither good nor bad any more than writing letters is.  It is the content of the message that is to be judged, not the act of sending it.  

Even in a "limited constituional government" lobbying would still be important.   Citizens have the right to call for or "block" legislation about all kinds of simply operational decisions, such as the architecture of courthouses, or the equipment of the military.  If you cannot be there, then hire someone to carry your message.