The spear really does disappoint. It should certainly have Defensive 1 minimum based on the description. I would think that a spear perhaps could benefit from an additional point of Pierce mechanically. I think a spear does give reach so the best I could think for this is if you were Engaged with an enemy using a spear they aren't Engaged with you and are still at Short requiring them to move to Engage (excluding Silhouette 2+).
For Summary Versus the Vibro-ax:
+200 Credits, +1 Rarity, +1 Advantage needed to Crit, +1 Defensive, +1 Pierce, No Sunder, Added Range.
That seems kinda fair mechanically and something about the flavor of being able to Spear someone before someone else can Ax or Sword you makes sense.