It is a little known (or maybe well known?) fact that the stock letters,
postcards, etc. you are talking about are very ineffective in persuading
political leaders.  Letters which are individually written, and well thought
out, are much more effective means of persuasion.
 
Anyone can sign a letter, petition, but someone who takes the time to compose
their own letter must be strongly committed to whatever issue they are
writing about.  Or so the thinking goes.
 
As a final note, a Senator I once was acquainted with was asked how  many
letters it took him to reconsider his position on a particular issue.  He
replied that 4 or 5 "well-written and well-thought out letters" would cause
him to at least reconsider his position.  Maybe he was a fluke ... or maybe
not.
 
Scott Wilhite, Director
National Museum of Roller Skating
Lincoln, NE