Everywhere you look there are problems in the world today ,drug addiction,cancer,global warming,exstinction of species, oil shortages ,food and water shortages in the third world the list is endless but only so many of these can be dealt with limited recources with money and political attitudes towards dealing with these and many other problems.
I don't think travelling into space for minerals would solve all the problems in the world and i don't think it would be very cheap either and thats what it would come down to how cheap and affordable it could be for the richer nations of the world.