I'd also like to suggest balancing the Void Pavilion Body Refinement. An item that improves +10 is 5x more expensive than something that improves +5. (i.e. +5 Swiftness is 10 MID stones, +10 Swiftness is 50 MID stones.)
They both have the same proportional increase to impurities. (+5/+5 and +10/+10)
I would suggest decreasing the impurity gain on the expensive item, or increase the stat gain to reflect the higher price. Otherwise, why would we purchase the more expensive item when it's 5x more expensive yet only 2x more gains?