I think it's definitely a matter of return.
For the same value coming back Kelly vs Boychuk is a no brainer, it's Kelly every time. Older, position where we have some depth etc. However, you're unlikely to get anything of value for him. On the other hand JB could fetch a somewhat decent return, IF you think you can replace him from within, which is obviously the million dollar question.
Are you going to get a durable, hard hitting, aggressive defenseman who is hardly injured and plays like a demon in the playoffs? No? Then I keep Manchuk, deal CK for peanuts and move on. In the playoffs we were desperate for veteran d, if they trade JB for MORE kids, Seids gets hurt in the last game of the season after yet another luke warm trade deadline in '15 and Kelly is still here tripping on his crutches and we go out in the first round (or not make the playoffs at all, Chia will be done like dinner here.
When you trade in your four year old car do you expect to get 99% value back? No, you got service out of it, drove it over some curbs and slammed it into "park" while still rolling...Someone else's headache now.
BTW: Maybe that car analogy is just me!?!