Personally, I like Vagner a lot. He's intelligent, smooth and strong positionally....when he's on. He's had serious bouts with inconsistency, which have put him in coach Benoit Groulx's doghouse the last two years. I really think he would have benefitted from a trade, because as amazing a coach as Groulx is, he doesn't like Vagner much it seems.
In this year's draft, I'd sign Vagner instead of taking the 56th overall pick. I still think Vagner could become a solid #4 defenceman, but he'd need a good first year in the AHL for sure. You aren't going to get a defenceman with more upside at 56 this year than Vagner, not close.