Simple NPC AI using Nav Mesh

Hi Everybody, Here is my problem. I've made a C# script to navigate a NPC(no animation yet, real simple) and if you look at my script you (should) see the problem.

 public class NPCTestNav : MonoBehaviour {
 
     NavMeshAgent agent;
     public Transform Nav1;
     public Transform Nav2;
     public Transform Nav3;
     public Transform Nav4;
     int RandomValue;
 
 
     // Use this for initialization
     void Start () 
     {
         agent = GetComponent<NavMeshAgent> ();
     }
     
     // Update is called once per frame
     void Update () 
     {
         RandomValue = Random.Range (1, 5);
         Debug.Log (RandomValue);
         if (RandomValue == 1)
         {
             //This is part of a code snippit and will wreck the code if uncommented.
                 //Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
                 
             Ray Position1 = new Ray (Nav1.position, Input.mousePosition);
             RaycastHit hit1;
             if (Physics.Raycast (Position1, out hit1, 1000)) 
             {
                 agent.SetDestination (hit1.point);
             }
         }
         if (RandomValue == 2)
         {
             Ray Position2 = new Ray (Nav2.position, Input.mousePosition);
             RaycastHit hit2;
             if (Physics.Raycast (Position2, out hit2, 1000)) 
             {
                 agent.SetDestination (hit2.point);
             }
         }
     }
 }
 

As you can see, it assigns a new Destination every few frames. I currently have only 4 destination points, but have not got that far yet, just trying to work out two points. So, my solution just add a simple script to get the speed of the NPC and then add an && to the if asking if the avatar is moving. However, whenever I try to add the code, it always comes up as not moving???? What is up here?

EDIT: Ok so to clarify, I want an NPC that will, every frame choose randomly with a 1in4 chance a new Destination unless it is already travelling to a destination. There is four destination points, these destination points are cubes.