The hero item Pouch of the Thief is not exactly the greatest hero item. A plunder bonus of 10-20% isn't exactly the biggest advantage in the world. After a while of the server the item becomes just something you buy for a 100 silver to fulfil the daily quest task of buying something on the auction.
To buff this item I would suggest adding the ability of the item to make the hero able to carry resources. I feel this would be a great addition to early game, I.e. the tier 1 item makes the hero able to carry 400 of each resource.