NQ/HQ Crafting mats should occupy one inventory slot each.

[ninjamatic]

All you have to do is indicate high quality items by putting a number on a different corner of the item icon. So bottom right for NQ, top left for HQ. Easy. Less clutter.

[Frizze]

That does sound easy enough from a graphical design perspective. One would imagine that programming a single inventory slot to accept more then one type of item at the same time is slightly more work.