Collider and Distance Problem OnMouseDown

I'm having some problems with the onmousedown event on some of my collider objects.

Here's two screenshots illustrating the problem:

Screenshot A: http://i.imgur.com/2IWzQXR.png

Screenshot B: http://i.imgur.com/NoEplyB.png

Some background on the images: This is procedurally generated roller coaster track along a hermite spline curve via the control points you see in yellow connected via a line renderer that is also yellow.

Screenshot A shows the distance at which I would like to be able to click and drag the control point, however it doesn't work.

Screenshot B shows how close I have to be to the object to get it to work. Notably I have to clip through the track.

Here are some caveats: There is no collider currently enabled on the track! The button in the bottom left "ride it" is what enables the collider. Does having it not enabled mean I can't look "through" it as if it weren't there in the first place?

If I try to click/drag outside the track on the exposed parts of the handles I can do it a bit further away, but still not as far away as I would like.

I'm thinking it might be that it is somehow seeing gui components, but it does still work close up. I fiddled with the clipping planes for kicks and grins but that wasn't it either.

Again, it works at pretty close distances but not far away. It needs to work far away. Below is relevant code.

 public class draggable : MonoBehaviour {
 Vector3 screenPoint, offset, scanPos;
 
 // Use this for initialization
 void Start () {
 
 }
 
 // Update is called once per frame
 void Update () {
     scanPos = transform.position;
 }
 
 void OnMouseDown()
 {
     print ("I see you");
     screenPoint = Camera.main.WorldToScreenPoint(scanPos);
  
     offset = scanPos - Camera.main.ScreenToWorldPoint(
         new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z));
 }
 
 
 void OnMouseDrag()
 {
     Vector3 curScreenPoint = new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z);
  
     Vector3 curPosition = Camera.main.ScreenToWorldPoint(curScreenPoint) + offset;
     transform.position = curPosition;
 }
 }

This code listens for a toggled bool in my gui script to disable and enable the colliders. This code lies on the gameobject that procedurally generates the roller coaster track.

     if(guiobj.riding) {
         collider.enabled = true;
     }
     else {
         collider.enabled = false;        
     }