In answer to your first question operating in First Class is a promotion from Economy. You have to pass a specific course for your upgrade to the first class service. I have never heard of anyone outside of VIP being offered a monetary gratuity although I have been offered a gift from the Duty Free service. A letter to compliment your service is far more appropriate and very gratefully received by both the company and the cabin crew. If one stands out then take his or her name as it goes on their file and all adds up when it comes to consideration for promotions.