わかるで？
using UnityEngine;
using UnityEditor;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

public class UIPanelDepthEditor: EditorWindow {

    [MenuItem("Window/UIPanelDepthEditor")]
    public static void ShowWindow() {
        EditorWindow win = EditorWindow.GetWindow<UIPanelDepthEditor>();
        win.title = "UIPanelDepthEditor";

    }

    void OnInspectorUpdate() {
        // reset collection
    }

    UnityEngine.Object target = null;

    void OnGUI() {

        bool isPanel = false;
        GUILayout.BeginVertical ();

        var replaceObj = EditorGUILayout.ObjectField( "ObjectField", target, typeof( Transform ), true );
        if (replaceObj != null)
        {
            target = replaceObj;
        }

        GUILayout.BeginHorizontal();
        {

            EditorGUILayout.PrefixLabel("Depth");

            if (GUILayout.Button("-10", GUILayout.MinWidth(46f)))
            {
                DepthControll((Transform)replaceObj,-10);
            }
            if (GUILayout.Button("Back", GUILayout.MinWidth(46f)))
            {
                DepthControll((Transform)replaceObj,-1);
            }

            var text = "";
            if (replaceObj != null)
            {
                var panel = ((Transform)replaceObj).GetComponent<UIPanel>();
                if (panel != null)
                {
                    text = panel.depth.ToString();
                    isPanel = true;
                }
                else
                {
                    var widget = ((Transform)replaceObj).GetComponent<UIWidget>();
                    text = widget.depth.ToString();
                }

            }

            EditorGUILayout.TextArea(text);

            if (GUILayout.Button("Forward", GUILayout.MinWidth(40f)))
            {
                DepthControll((Transform)replaceObj,1);
            }

            if (GUILayout.Button("+10", GUILayout.MinWidth(40f)))
            {
                DepthControll((Transform)replaceObj,10);
            }
        }
        GUILayout.EndHorizontal();
        if (!isPanel)
            EditorGUILayout.HelpBox ("これはUIPanelじゃないです", MessageType.Warning);
        EditorGUILayout.HelpBox ("UIPanel以下のUIWidgetをまとめてDepth操作する。\n　ちょっと重たい", MessageType.Info);
        GUILayout.EndVertical();
    }


    void DepthControll(Transform obj,int depth)
    {
        foreach(var child in obj.gameObject.transform)
        {
            var item = child as Transform;
            var widget = item.GetComponent<UIWidget>();
            if (widget!= null)
                widget.depth += depth;
            else
            {
                var panel = item.GetComponent<UIPanel>();
                if(panel != null)
                    panel.depth += depth;
            }
            DepthControll(item,depth);

        }
    }
}