One extension of the basic triangle, which I picked up from the Puzzle Strike community, is that players' strategies are moving around the triangle in response to each other and so good players will 'dance' their development from one corner to another as their opponents' strategies are revealed; defending, but shifting to economy as the opponent backs off or building up a counter-offense, and sometimes ending up in a winning position by performing that shift too quickly for the opponent to scout or respond to.
Another extension is the notion of dominance, where past successes protecting and using your economy and destroying the opponent's assets can just put you ahead of your opponent on one axis despite your triangle stance leaning the other way, so that if you get far enough ahead you can have more economy and more defense and more offense all at the same time. Triangle dominance is effectively a looming win condition that forces your opponent to do something extreme to pull ahead in at least one axis because any compromise loses.
