Yup, that "not" would block it. I will have to make that more clear in the EDB Guide when I get time.

If you want to not allow sparta to have walls then make a resource necessary for walls. Doing it your way will also mess up the building browser (a pet peeve of mine btw). ;)

You might use "slaves" as a resource as it is assigned to all regions usually; and getting rid of it in sparta will not hurt.