You could farm floodplains until you grow to a decent size and then replace them with a Kasbah. And 1 food for a production and gold is pretty useful. Though spamming them will hurt your ability to counterattack as the AI will get the fort bonus too.
I think an interesting ability (missed opportunity) for the Berber Cavalry in lieu of the friendly territory bonus would be to receive defensive bonuses. That way there's synergy with all the Kasbahs that will be covering your territory.