Site not getting correct featured image from my query

You are supplying a meta_key but I think you need to give a meta_value. See this article for more information. I realize some things may have changed in 3.5, but this doesn’t seem right to me.
http://codex.wordpress.org/Class_Reference/WP_Query

If you want to get featured image, why not use something like this then?

if ( has_post_thumbnail() ) {
    the_post_thumbnail( 'medium', array( 'class' => "medium" ) );
}

EDIT: adding more specific use case:

if ( has_post_thumbnail() ) {
    $thumb = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'homethumbs' );
?>
<a href="https://wordpress.stackexchange.com/questions/76518/<?php echo get_posts_page_url(); ?>" title="Visit the Serge Blog" id="homelink3" class="top_homelink">
    <img src="<?php echo $thumb[0]; ?>" width="308" height="308" id="home-blogthumb" class="side-homethumb wp-post-image" /> 
    <p class="home_text">Blog<br/><span class="home_thumb_caption">Latest Post: <?php the_title(); ?></span></p> 
</a>
<?php } ?>