I like the idea of the duplicate items feature although it doesn't really duplicate the item right now, but takes another from your bag and gives it the same scale/orientation.

I feel it would be better if it actually duplicated the item and if necessary charged you the cost of the item per duplication with a simple OK / CANCEL interface menu. This would mean that if I was say, building a staircase, I would need only one plank item in my bag and could buy more as required while building without having to leave my dimension and buy more planks from the vendor.