I know it's an old tread, but it is a relevant debate. I have found spy defense towers to be helpful as a tool against stripping. But, with attack you were protected by the DTW rule at 20%. The defense tower may be more useful if the devs actually remove the 20% DTW rule and punish for going to 0% stats. In the end, this is more of a discussion for larger builds as u need the $ from buildings to get the highest cost lands. You can convert them to towers later on basically, if needed.