add_action( 'admin_bar_menu', 'remove_nodes_mysites', 999 );
function remove_nodes_mysites( $bar )
{
    $sites = get_blogs_of_user( get_current_user_id() );
    foreach ( $sites as $site )
    {
             // Open Visit Site in new window/tab
             $visit_site_node = $bar->get_node( "blog-{$site->userblog_id}-v" ); // Visit Site
             $visit_site_node->meta['target'] = '_blank';
         $bar->add_node($visit_site_node);
    }
}

add_filter( 'myblogs_blog_actions', 'my_sites_visit_site_target_blank', 10, 2 );

function my_sites_visit_site_target_blank( $actions, $user_blog ) {
    $to_replace = ">" . __( 'Visit' ) . '</a>';
    $to_replace_with = " target='_blank' >" . __( 'Visit' ) . '</a>';
    return str_replace( $to_replace, $to_replace_with, $actions );
}