The consensus around the league, at least until Witt showed up, was that the Preds were a highly skilled somewhat soft hockey team. Why not change that image with a trade for Pronger. He is argaubly the best D man in the NHL, tough and plays exactly 1/4 of all of the minutes that your efense have to play each night. He is a noticeable upgrade on the Preds existing D and gives a very good team the chance to go as far as the Oilers did in the Stanley Cup finals.
Plus the Preds are not that young ateam.
Expensive? Yes but at what cost? Likely the Preds best Dman, Hamhuis, a top 6 forward (Hartnell) and a prospect- Weber , Radulov or Upshall