Good suggestion!
You'll have to get your hands a little dirty, but you can disable sending attachments in invoice delivery emails by commenting out lines 80 - 85 in /components/invoice_delivery/invoice_delivery.php
$attachments = array(
/*
array(
'path' => $inv_path,
'name' => $attachment_name,
'encoding' => "base64",
'type' => $this->company_settings['inv_mimetype']
)
*/
);