Well, which luxury food? If a food is difficult to get hold of, say, because of trade disagreements, its rarity could make it a luxury. In WW2 Britain, oranges were a tremendous luxury for they, and many other foods, could not be obtained. Ships that would normally bring the freight were shot down before they reached Britain. Foods that might once have been regarded as utter luxury, say a rich chocolate cake with cream filling, is now so widely available that is it a luxury anymore?
Truffles are still rare, because there are only a few places and times that boars can snuffle them out. Therefore they are a luxury. As for over-rated, well if you don't like the taste, yes, over-rated. But if you just love and yearn for them, and are told they are bad for your health, they do not seem over-rated at all.