If you add the following to your plugin then people will be able to use the shortcode [wowhead]itemnumber[/wowhead] in their posts. This may or may not be easier than adding the full link.
function wowhead_shortcode( $atts, $content = null ) {
return '<a href="http://www.wowhead.com/item=' . $content . '"></a>';
}
add_shortcode( 'wowhead', 'wowhead_shortcode' );
You might also want to change the var to
var wowhead_tooltips = { "colorlinks": true, "renamelinks": true }
so that people don't have to add the name of the item and so that it is colored according to quality.