How something is cooked and what it's paired with greatly affects my opinion of it, so I don't think I could make such a sweeping generalization of a type of food like wagyu. By the way, "wagyu" tells you nothing about the quality of the beef. All Japanese beef is wagyu beef, that's the type of cow. However, not all wagyu beef is graded at A5, nor is it all from the same part of the cow.
Anyways, the only way I'd be able to say something is overrated is if it comes from a particular restaurant, and is generally prepared the same way(although, again, how well it's cooked matters). Popeye's spicy chicken sandwich comes to mind. It's a decent sandwich as far as fast food goes, but I don't think it's any better than something like Chic-Fil-A.