Remarkable 1: remittances of immigrants from third world countries form a substantial part of the GDP for most of those countries. In some cases this money flow is even the biggest, or almost the biggest part of the GDP! see ILO site. One recommendation to labor-exporting countries is to introduce micro-finance intermediaries, because savings/remittances of their expats are not always invested well. Expats are not always also good enterpreneurs.
Remarkable 2: Moving all trade barriers would be benefiting for most African countries, with the exception of eight. For those, more competition would lead to higher import prices because they cannot produce enough added value. See LEI (Wageningen Univ.)