[JeffF.]

By this time not many of the Noldor who made the journey to Aman and saw the Light of the Trees would have been left. As Gandalf described Glorfindel those elves who saw that light had a power in the unseen world that Dark Elves did not. Most of the remaining Noldor would have been those born in Middle Earth and never saw the Light. As Glorfindel told Aragorn there were few even in Rivendell who could ride openly against the Nine.

Obviously assassination was not a tactic that would occur to the 'Good' but thinking back through the books it does not seem to be a tactic used by Morgoth or Sauron either. It is not the taking of the lives of those opposed to them that is their objective what they cannot tolerate is Free Will. Morgoth and Sauron must dominate everything and everyone and to do that they don't assassinate. Think of Hurin, captured after the Battle of Unnumbered Tears, this most powerful warrior of men is twisted and corrupted rather than outright killed.

The Lord of the Nazgul could easily have killed Frodo with the thrust of his Morgul blade instead he wounds him in a way that will bring Frodo under his will. both sides kill in open battle and in duels (Fingolfin and Morgoth - elendil/Gil-galad and Sauron) when necessary but assassination is not a method for either side.