All the files listed in the plugin could be placed on the file server to help - but part of your delay may simply be the browser doing all required rendering work.
In your plugin definitino you modify #PLUGIN_PREFIX# with your #IMAGE_PREFIX# location.
I have a folder dedicated to plugins.
Navbar 1.2 may not work because of newer libraries available in APEX 4.2 that aren't in 1.1, but that's a guess.
The browser is displaying the unstyled content of the generated menu because the CSS required by the plugin is not in the page header where it should be. See this thread for discussion on how to move the style sheet(s) to improve the rendering.