I don't personally think that Ennis is worth a top five pick. But I really wouldn't be willing to move him unless the return is drastic. My personal favorite Sabre. Never has issues with effort or ability.
Ennis has talent, loads of it. The problem is, where does that talent fit?
On the powerplay it works, Ennis is great in open ice. 4 on 4 - give me Ennis.
The problem with Ennis is where does he fit on a line? and how do other teams match up?
He's not a first or second line center. (not yet, anyway)
He's an undersized winger that gets easily knocked off the puck. (he does get up right away however)
In a tight game he's not the guy to have out there defensively in a strong checking role.
So for most coaches, Ennis is a bit of a conundrum, you love his talent, but finding the right line and time to exploit his talent is going to mean constantly shifting him around. So it is hard to build a team around him. He can't be part of your core. He's a weapon, not an anchor for a line. That's why his trade value is pretty limited.
This last season was very much about whether or not Ennis could succeed at center. The answer seems to be mixed.
On a poor team Ennis can put up 50-60 pts a year in a top 6 role - but percentages are bad that you win the match-ups.