@fBoyle-- I don't see things that way at all. There is definitely a connection between education and economic growth. I think the issue with studying the relationship is that the effect takes time. Education encourages economic growth in the long-term and the effect isn't as noticeable as some other factors like investment, so it's difficult to measure.
Think of it this way, there are several major factors that lead to economic growth. These are: resources and innovation. Considering that a developed nation like the US has already discovered its resources and using them fairly efficiently, the biggest factor that can boost economic growth is innovation. I'm talking about technology -- new and better ways to do things. And guess what? A nation that is not educated cannot innovate. So education is immensely important.
And just to let you know, defense, security and stability are just as important for the economy.