Look at it this way: Do you expect Nash to score MORE than he has on a good team? Will he improve by more than 5 goals a year? if so, you've got a potential 40 goal scorer or more. That will put him in the top 5 of goal scorers any year. 3-4 Good players/picks, might be worth it to get one great guy in the top 5 of scoring.
Or, conversely, will he be like Kovy and see his production go DOWN when he is not the sole goal scorer on the team? in that case, he might not be worth the cost.