I'd ask where you are getting those numbers from, but I already know.
First, his value isn't 110% right now because of the injury. Second, his value isn't going to drop to 50% simply because he only has 1 year left on his contract instead of 2.
If Staal comes back healthy, stays healthy and plays well next year, his value will be much higher than it is right now, regardless of his contract situation. How many years he has left on his contract doesn't mean much if he wants to go to carolina and carolina wants him. Jordan only had 1 year left on his contract and that didn't hurt his value at all.
The one and only reason you want to make this deal now is because carolina has the 5th overall pick, and the shiny new toy is more appealing to you than the one you have.