The answer? It depends if you have a salary cap. If there's no cap and you have virtually unlimited revenue - which has been true of many teams at many times - then the key to winning is having the best possible players at every position. It doesn't matter if the New York Yankees can overpay Alex Rodriguez and Mark Teixeira - all that matters is that they produce the maximum number of runs possible at their positions. As long as they're the best and you have the money, you should keep them.
But in the NHL, the story is completely different - it's all about spending efficiently. Let's take Drew Doughty, for example. Compared to free agent defensemen, he has probably been worth $15-20 million dollars to his team over the last two years. He's been paid all of $7M. He could easily be worth $30-$40M over the next four years; between his last UFA year and his first three RFA years, he might make another $20-25M. So Doughty is worth somewhere between $5M and $20M to his team compared to what his replacement would cost on the open market (this is his 'surplus value.')
As the Chicago Blackhawks showed, one of the keys to winning is to have a bunch of entry-level and RFA contracts on the books, so that your players are producing more value than they're being paid to do. So Doughty probably has as much surplus value as any player in the NHL - does that make him untouchable?
Not a chance. But the price is steep: if the Atlanta Thrashers or the Edmonton Oilers offered you all of their draft picks for the next three seasons, Doughty still might be more valuable. In fact, short of another team taking all of your bad contracts off your hands and giving you all of their draft picks, there may not be a set of assets in the entire NHL valuable enough to move a 20-year-old superstar.