While I agree that they are longshots in becoming impact players at an NHL, I completely disagree that it is a waste of time. For a potential diamond in a rough like Tyler Bozak or Teddy Purcell, it is a useful endeavor to sign these college agents especially when they cost nothing but a roster spot. Even if you can find a depth character player for free, it is already worth if.
Here's an article about the topic.
http://eyeonthesens.com/2013/09/02/f...t-nhl-updated/
I think the key message is expectations. You don't sign these guys expecting them to have an impact. You sign them and if they pan out, great, but let them go if they don't.