Dunn would be an upgrade over MCW from a shooting standpoint. He is also a relatively tall point guard which seems to be what the Bucks want.
Vaughn could be the outside shooter with Middleton, but he is still really young. Injuries to Vasquez and Mayo haven't helped, but not sure they are long term pieces.

I think our offense would be upgraded with Dunn, and I really don't think it would affect our defense at all.

Possible you don't really need a true center to compete at a high level, but you would need at least an inside power forward / center to go along with Parker.

Do the Bucks have trade pieces should they want to move up a few slots in the draft? Is Henson worth moving up two slots? Is MCW?

I really don't think you can win with MCW, Parker and Giannis all on the court unless one of them really improves outside shooting (which can happen). For that reason, if they don't turn things around this year, and can get Dunn, I'd think MCW could be on the trade block.