Presumably the club has an idea about who it is chasing in the draft. It seems to me that the crop of likely local kids (your Williamses, Van Rooyens, Amisses, Erasmi) are all ranked between about 10 and 25. So it might be that hanging on to pick 6 (from Carlton) might be less important than say getting hold of a couple of picks in the teens or low 20s. Personally if we could land (1) Neale, (2) Johnson or Erasmus and (3) Amiss, Williams or Van Rooyen, then we're good. Especially if we can find a hidden gem or two further down the list.
So for example
Cerra to Carlton for 6 and 25.
6 and next years first round to Brisbane for Neale and 14.
Leaves us with 8, 14, 25, 27.