Crafted gear is upgraded by recrafting with enchanted crests you purchase off a vendor. Instead of incremental upgrades, it goes up in one shot to the maximum for that enchanted crest.
So if you have say a 658 item level piece and you upgrade it, it goes straight to 675 (or 681 with the Turbo boost augmentation device). That’s why valorstones and crests aren’t applicable.
The enchanted crests you purchase have crest costs, but a lump sum versus incremental steps.
Given the proper number of crests, i.e. 60 gilded, you can craft a brand new item straight to 675.