How to find out if page_for_posts is showing (in order to style menu item)

I think this should work if you are wrapping the condition around the arguments, and not the menu link itself:

if(!is_user_logged_in())
{
$args = array(
'exclude'      => '100,110,145'
 );
}
else
{
$args = array(
'exclude'      => '100,145'
 );
}

wp_list_pages( $args );