Is there a way in advanced XML to show the last refreshed date on a dashboard? Its important to show the refresh date on panels using cache especially since they are displaying relative time almost all of the time.
There certainly is.
It's just that the presence of that "last refreshed" header is dependent on there being a title for the dashboard panel. If there's no title bar at the top of the panel, there'll be no last-refreshed information.
Put a group="My dashboard panel" attribute on the module where you're defining your layoutPanel and you'll get a last refreshed header.