I think your assessment of where the team currently sits is incredibly off base.
First, with league average goaltending, they beat the Rangers in 5 or 6 games. That puts them against Carolina, a very winnable series. They might not have beaten Tampa, but this team was league average goaltending away from being one of the Top 4 teams in the league this year, even with an aging core. You don't tear it down prematurely when you're that close to playing for the Cup.
Second, the nuclear method isn't as successful as the Penguins have made it look. For example, if the Penguins had begun dismantling the team last year like you suggested and begun to stockpile draft picks, they'd be picking in two of the shallowest drafts in recent years. None of the top picks recently have rated as an Ovechkin, Malkin, Crosby, etc. type. Bedard does next year, but there is no guarantee that the Pens would get the top pick.
Third, you may point to the Wings, but I point to the Kings. After a couple early exits following their Cup, they began to emphasize getting younger and missed the playoffs three years in a row. They kept their core of Doughty, Kopitar and Quick, brought in younger players, and are now on the rise again behind guys in their mid-to-early 20s with their older core still playing major roles.