These plugs are low risk, high reward bets made by GMs. A lot of players on that list have caught fire and helped their teams for a season or two or even just a couple months, whether it was for the Devils or not. That's worth it when you pay essentially nothing for a boost that might be the difference in making the playoffs or not (obviously one of many factors). By its very nature, there are more misses than hits. Carrick, Agostino, etc. are fact-finding missions. Agostino is a good 4th line add and/or competition for kids.
You make these bets when your drafting sucks or your pool is too young and isn't graduating guys fast enough. We've got players incoming and they're taking spots (Coleman, Wood, Bratt) and now Anderson, Bastian, McLeod, etc. But the latter group will have their ups and downs and need to take a seat for a stretch - that's when your vet in the press box is a useful plug.
We're doing what you're saying, but it takes time.