Just do the math. I dont remember exactly how many lands i had at the time, but in a nut shell.. For me to get 1mill more in my spy attack, going with the cheapest upgrade/land was going to cost me 4trill. Saving a little more and buying the more expensive build/land would only cost me 1.5trill. Buying whatever is cheapest is not always the smart plan. In fact it can be one of the worst possible things you can do.
Oh yeah and this thread is worthless now that I'm an Sh and not even an attack build. A mod can lock this