Banal pleasantries cost nothing (less than nothing with this new feature), and at worst are ignored and at best make the receiver feel better about you and the important text that follows.
They can have a cost if they dilute the core intent or message of the email: the reader has a higher cognitive overhead before understanding how to reply or what action to take. I spend a lot effort stripping out fluff and filler fron my mails, as a courtesy to the recipient!
