Actually, Sinai and Cyrenaica are very much worth developing, for excellent Mamluk Horse Archers and Saharan Cavalry, respectively. When I play Egypt, I find myself finishing the castle in Sinai before anywhere else to get my hands on some great mounted archers. And Valor 2 Saharans are scary, fast and deadly. Fantastic medium cav and very, very cheap, and available to all Muslim factions.