It all vendors for the same price though, regardless of ilvl. So as long as you have enough boxes at 100 to get a complete set, the occasional upgrade might be worthwhile just so you can survive more easily. I was able to get a complete set of warforged at either 710 or 720 when I got to 100 with about 50 of each box. In the end you're going to vendor most of it anyway since you only need 1 of each piece.