It's not that people overvalue them. It's that the truly elite guys are essentially priceless. Unless something happens where they force their way out (Roy, Pronger, Martin St. Louis), have some kind of injury that calls into question their future value that they then push through in recovery (Gretzky to NYR, Gretzky to STL), or they have an ultra cheapskate owner who just wants the $15 million that came with it (Gretzky to LA)... guys like this don't get traded.
They never go for as much as fans expect because you don't trade one of these guys unless you have a figurative or literal gun to your head. It took Roy bitching directly to the owner after being pulled, Pronger... complaining, don't really remember what he did in Edmonton, but it was something, and Martin St. Louis being super salty with Yzerman. Hell, Gretzky wasn't traded. He was sold. LA doesn't land that trade in current day, because Peter Pocklington couldn't sack away 5x a player's salary in cold hard cash nowadays.
Whenever someone gives you an offer where they're asking you for 5 blue-chip pieces AND other stuff... just assume they don't want to trade the guy and he's not available.
