Resources for understanding long term livelihood change are gradually growing. Here are some useful websites, with a focus on Tanzanian data:
The Kagera panel: Circa 6,000 households surveyed 1991-1994; 2004; 2010.
The Living Standards Measurement Survey: From many countries, hosting Tanzanian data from 1993, 2008-9 and 2010-11 and 2013-14.
The 'Microdata site': Hosting diverse surveys, with numerous Tanzanian data.
The 'AFRINT' study collected from 6 countries in 2002 an 2007,8 and 2016. We are collaborating with this project.
The Demographic and Health Surveys, including asset data from over 90 countries and 300 surveys. A cleaned version of these data used and prepared by Alwyn Young are available from his website.
The official site is here