They pay okay gil, nothing really helps the gil flow.
They build at the same rate they did before, 3 every 12 hours. Up to your maximum again.
People say to save them mostly because they are best for gathering and crafting. They are horrible for combat classes. it's really up to you if you want to do them for those, but you will get bad xp for the effort. They are great for gathering and crafting since you can turn in HQ items and basically get 3x the xp for it, three times. Those sometimes let you turn in extra items, and when you turn in HQ, it's a LOT more than normal, and some let you turn in even more a couple times, giving you even more. You can easily get a level or two doing a couple of those if you plan them right.