TWU, I`ve been playing Maru for ages, and I`ve always gone Housing/Agri. =P
To the OP: Even if you are going completely Plunder/Housing (which on fast, with the food market stagnating low, I`d recommend) it`s still a good idea to have the U.Fert as you`re base Colony. Protects you from being caught unable to plunder down to NP, and will always generate at least a small amount of food for you (except when popping up captured colonies, obviously.) Still, even as a primarily plunder based Maru, I find it a good idea to have ten or so levels of Agri infra, along with a U.Fert. But that is just me.