I can seem to remember that wearing of our badges on flights were recommended after 9/11, to show the passengers that if we thought it was safe enough to fly, then they should be safe too. So if its good enough to wear then, I don't see any reason why it shouldn't be good enough now or anytime. I don't wear it myself while flying, but I did after 9/11 to go with the flow. I don't recall getting free drinks over it unless I was up in first class with or without a badge.
I never buck for free drinks. In fact, it seems to me that FA's like to push drinks on me while riding in first. Almost recommending me to have one. "COMON, IT WILL RELAX YOU"...But down in coach, I just take the free soft drinks or water. I never pay the five bucks for a canned beer.