Yes. I believe that economies and migrant workers will benefit from the UN convention, but I believe this with one caveat. The migrant workers will not want to feel regulated in their efforts to make a living. If the UN imposes limits and regulations on migrant workers and their employers, this will deter migrant workers from being able to work as much as they would like to. Sometimes a decent "under-the-table" wage is great for an economy. I'm not saying they should be doing this, but it definitely makes a difference in terms of how much money a migrant worker is able to send home to his or her extended family.
No, the UN Convention on the Rights of Migrant Workers and their Families is not good for economies, because it is too specific. What is good in one country might not be good for another. Each nations needs to develop their own policies, based on what their own economy can sustain. It is unfair to make all of the nations the same.