I think you got the Rangers mixed up with the Islanders, after all the Rangers made the playoffs the last 4 years.
Redden and Gomez turned out to not work, though Redden played fairly well in last years playoff, but he was able to trade Gomez and probably will be able to trade Redden somewhere down the line. Shanahan played pretty well and it was Sather that didn't want to pay him for another year. The other players where before the salary cap was in place and some of them actually did performed fairly well. As for defense, well under Renny they were a really good defensive team, problem was they couldn't score enough. The team right now has quite a bite of young players, especially on the blue line, which should help their power play, but it will take time to develop them. As for the salary cap, I'm pretty sure the Rangers actually have room under it right now.
Leetch and Graves where old, he got value for them which is better then keeping them to mentor players. As for Prucha and Moore, neither was playing and when they where they didn't produce.