Sending youth on missions is a chance to expose youth to other cultures and see how the poor live but as far as being useful to the population of the missions visit is certainly up to debate.  Having a daughter that lived in Honduras and Chile for 7 years she witness up close the many groups of kids that came through.   You can only build and paint the churches so many times and in most cases the mission groups rarely even asked what the locals want to be done.  You have to remember that every branch of church sends mission to country they may have some interest in converting people to their faith.  The folks in Honduras in those days were much more interested in having a building constructed to store grain then another church constructed, you may recall these people do have a religion and were not in need to be converted.   The money that it took to send these kids to South Africa was huge you have to think it would have accomplished more to just give them the money instead.