Currently recipes are pretty poor investments. You can not upgrade another person's bound items. Following WoW's enchanting pattern would make sense for this. There should be a slot in the trade bar that is temporarily accessible for the purposes of upgrading items. That way a player can apply a recipe as part of a trade (being able to modify but not get the other player's bound item), and rare recipes become interesting and worth getting.
And remove the primary crown sink from the game? You have to remember that there are VERY few pieces of equipment in this game for an MMO.