While untradable items would surely limit the ways of obtaining the item, the item value itself really depends on what it does.

If the item is only for vanity, like the event items, then it won't really hold the attention of any crafters at all. It'll just be craft it once, and never touch it again.
If the item was a consumable, like lets say the Keeper's Hymn, which resets your class stats, then it'll have a longer life span. Though, a bad item example, since people usually don't keep resetting stats.

Even though it is self-serving, it needs to have something to keep the crafter wanting to keep making it.