Having had Porcupine for over 350 hours, here are some upgrades that wouldn't make it overpowered.

1) Slight Incarnadine Effect to quill damage
2) Include quill damage for Kick, Bash and other abilities that bring the body into contact with the Porcupine
3) Edge: Elongated Quills (Remove the Negate Effect of 2-handed swords, maces and axes.)
4) Increase natural damage reduction
5) (MOST INPORTANT) Remove the variant damage. Porcupine is the only thing in game thats possible of doing a maul and a DEVESTATE in the same round to the same mob.

An aside request. Lower the damage reduction on the Destructor. It seems every time I try to raid, the damage reduction is increased.