this is a bad idea. devaluing the HQ items considerably is not an option.
I think either the addition of a desynth for NQ items is a good idea to remove these items from the economy. but instead of having that powdery thing to empower future synths, i think a system such as aions enchanting cwould be a good idea.
If youre not familiar with it, you basically can DE any item to get a stone of certain level, which can be used to enchant your armor and weapons for additional stats. When you fail that enchant, you lose part of that additional bonus and have to try again tho.
This adds a new market that adds consumables worthy enough to buy, risky enough so that you have to spend good money to get your enchanted weapon to max level, and takes care of the excess by destroying the armor/weapons no one wants.