Making HQ items might result in a 1 - 2 tome bonus per craft so people just don't farm NQ to cap tomes.

These tomes would be spendable on new items that can only be crafted. As an example, you might have a iLvl120 Chest Piece you can craft that takes 380 Crafting Tomes to make, along with multiple other mats.

If you fail to synth the item successfully, you keep the tomes, but lose all other mats. This is to ensure you can get items with the tomes earned each week, but there is a penalty to screwing up your crafting of it.

Items created this way would be bind on create. In other words, you cannot sell them or trade them to other players. It is your item permanently.