Storing User Settings

I mentioned last week I want to store all settings for my application as user settings so I won't write to app.config and require administrative privileges.  I didn't like the constraints imposed by the .NET Settings implementation, such as configuring user settings at compile time and using attributes.  After implementing my own key value store implementation I'm realizing I may use the .NET settings provider for application settings, since I want it strongly typed, to have default values, and to have validation, and my property bag like implementation for storing settings application extenders write. For example Jane user writes a plugin and can persist settings in the user directory of my application.  This scenario doesn't work using LocalFileSettingsProvider.

Here is my initial key value store implementation:

using System.Configuration;
using System.Xml;
 
public sealed class DebuggerSettings
{
    public string this[string propertyName]
    {
        get
        {
            var store = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.PerUserRoamingAndLocal);
            UserSettingsGroup values = (UserSettingsGroup)store.SectionGroups["userSettings"];
            if (values == null)
            {
                return null;
            }
            ClientSettingsSection myValues = (ClientSettingsSection)values.Sections[typeof(DebuggerSettings).FullName];
            if (myValues == null)
            {
                return null;
            }
            SettingElement setting = myValues.Settings.Get(propertyName);
            if (setting == null)
            {
                return null;
            }
            string returnValue = setting.Value.ValueXml.InnerText;
            return returnValue;
        }
        set
        {
            var store = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.PerUserRoamingAndLocal);
            UserSettingsGroup addSectionGroup = (UserSettingsGroup)store.SectionGroups["userSettings"];
            if (addSectionGroup == null)
            {
                addSectionGroup = new UserSettingsGroup();
                store.SectionGroups.Add("userSettings",addSectionGroup);
            }
            string sectionName = (typeof(DebuggerSettings).FullName);
            ClientSettingsSection clientSettingsSection = (ClientSettingsSection)addSectionGroup.Sections[sectionName];
            if (clientSettingsSection == null)
            {
                clientSettingsSection = new ClientSettingsSection();
                clientSettingsSection.SectionInformation.AllowExeDefinition = ConfigurationAllowExeDefinition.MachineToLocalUser;
                addSectionGroup.Sections.Add(sectionName, clientSettingsSection);
            }
            SettingElement addMe = new SettingElement(propertyName, SettingsSerializeAs.String);
            XmlElement element = new XmlDocument().CreateElement("value");
            element.InnerText = value;
            addMe.Value.ValueXml = element;
            clientSettingsSection.Settings.Add(addMe);
                
            store.Save();
        }
    }
}