I basically d/e anything in outlands that isn’t soulbound. The reason why is because I’m always making money in some way. Vendor loot, sell off extra cloth, quest money, etc. But I can’t always get enchanting mats for the enchants I want…and I definitely don’t want to buy it instantly in the AH at some inflated price when I’m in town and need an enchant.
So I slowly build up my mats, and I know that it will go fast as I get an enchant or two, but at least I didn’t have to buy 50 arcane dusts at 60-100g out of pocket at AH. In that sense, I feel like I’ll save money over the long run even if vendoring the 8g item is a nice 8g in pocket, rather than just 2-3 arcane dusts. However, as others said, weighing the potential of the vendor money versus the dust price on your server, it may be better to sell the item off. 8g might represent 8 arcane dusts you could buy, instead of just 3 real dusts that you got.
As you know from doing so much d/e, weapons tend to give better mats than armor, and higher level stuff (say, 65+) tends to give more mats than lower-level stuff that d/es into the same mats.