Unity extension methods for SerializedProperty to get instance references and deal with arrays.

Ext_SerializedProperty.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEditor;
using System.Reflection;

namespace UnityEditor {
	public static class Ext_SerializedProperty {
		const BindingFlags FLAGS_ALL = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.FlattenHierarchy;
		/// <summary>
		/// Get the object this property
		/// </summary>
		public static object GetObject(this SerializedProperty p){
			object o = p.serializedObject.targetObject;
			// Friendly array syntax - one . per path element
			// e.g. propName.Array.data[0] => propName[0]
			string path = p.propertyPath.Replace(".Array.data[", "[");
			string[] elements = path.Split('.');
			for (int i=0; i<elements.Length; ++i){
				if (p.IsArrayElement(elements[i])){
					string arrayName;
					int j = GetArrayIndex(elements, i, out arrayName);
					var fi = o.GetType().GetFieldPrivate(arrayName, FLAGS_ALL);
					var arr = (System.Array)fi.GetValue(o);
					o = arr.GetValue(j);
				} else {
					var fi = o.GetType().GetFieldPrivate(elements[i], FLAGS_ALL);
					o = fi.GetValue(o);
				}
			}
			return o;
		}
		public static bool IsArrayElement(this SerializedProperty p){
			return p.propertyPath.EndsWith("]");
		}
		public static bool IsArrayElement(this SerializedProperty p, string path){
			return path.EndsWith("]");
		}
		public static FieldInfo GetArrayField(this SerializedProperty p){
			return p.GetArrayField(-2);
		}
		public static FieldInfo GetArrayField(this SerializedProperty p, int pathElement){
			// Friendly array syntax - one . per path element
			string path = p.propertyPath.Replace("Array.data[", "[");
			string[] dirs = path.Split('.');
			// If index negative, count from end
			string fieldName = pathElement < 0 ? dirs[dirs.Length-pathElement] : dirs[pathElement];

			var t = p.serializedObject.targetObject.GetType();
			return t.GetFieldPrivate(fieldName, FLAGS_ALL);
		}
		static FieldInfo GetArrayField(this SerializedProperty p, string[] pathElements, int elementIndex){
			// If index negative, count from end
			string fieldName = elementIndex < 0 ? pathElements[pathElements.Length-elementIndex] : pathElements[elementIndex];
			var t = p.serializedObject.targetObject.GetType();
			return t.GetFieldPrivate(fieldName, FLAGS_ALL);
		}
		public static int GetArrayIndex(this SerializedProperty p){
			// Remove cruft
			string path = p.propertyPath.Replace("Array.data[", "");
			path = path.TrimEnd(']');
			string[] dirs = path.Split('.');
			// Final element should be array index
			return int.Parse(dirs[dirs.Length-1]);
		}
		static int GetArrayIndex(string[] pathElements, int elementIndex, out string arrayName){
			// Find opening array bracket to get first element of int substring
			string e = GetElement(pathElements, elementIndex);
			int first = e.Length-1;
			for (; first>=0; --first){
				if (e[first] == '['){
					++first;
					break;
				}
			}
			// Name is substring from [0] to [first-1] (remove [{index}])
			arrayName = e.Substring(0, first-1);
			// Get substring from [first] to [penultimate element] (get int within [])
			int len = e.Length-(first+1);
			return int.Parse(e.Substring(first, len));
		}
		static string GetElement(string[] elements, int index){
			return index < 0 ? elements[elements.Length-index] : elements[index];
		}
		
		public static FieldInfo GetFieldPrivate(this Type t, string fieldName, BindingFlags flags){
			flags |= BindingFlags.NonPublic;
			FieldInfo result = null;
			Type type = t;
			Type bt = typeof(object);
			while (type != bt){
				result = type.GetField(fieldName, flags);
				if (result != null) break;
				type = type.BaseType;
			}
			return result;
		}
		public static PropertyInfo GetPropertyPrivate(this Type t, string propName, BindingFlags flags){
			flags |= BindingFlags.NonPublic;
			PropertyInfo result = null;
			Type type = t;
			Type bt = typeof(object);
			while (type != bt){
				result = type.GetProperty(propName, flags);
				if (result != null) break;
				type = type.BaseType;
			}
			return result;
		}
		public static MethodInfo GetMethodPrivate(this Type t, string methodName, BindingFlags flags){
			flags |= BindingFlags.NonPublic;
			MethodInfo result = null;
			Type type = t;
			Type bt = typeof(object);
			while (type != bt){
				result = type.GetMethod(methodName, flags);
				if (result != null) break;
				type = type.BaseType;
			}
			return result;
		}
	}
}