I had always assumed that the Great Wall strengthens you only against barbarians (and forces other civs to make peace with you), and I seldom build it, but according to the civ2 War Academy it does give you the benefits of city walls in all your cities:
http://www4.ncsu.edu/~jjseater/PDF/Civilization/Civilization2FanaticsManual.pdf (see chapter 1, page 2, which ios actually page 3 of the document). Is that info wrong?
http://www4.ncsu.edu/~jjseater/PDF/Civilization/Civilization2FanaticsManual.pdf (see chapter 1, page 2, which ios actually page 3 of the document). Is that info wrong?