I was going to say you got it exactly wrong (again), but that would only be true if your post ended at "Afghanistan".
DrNo:
At what point should America stop throwing money at Iraq, Afghanistan, the mid-east, the rest of the world, the flawed vision, the failing economy, and just sit back and say "enough"?
Diminishing Returns probably does fairly apply to the overall policy, especially since WW2 say, of aggressively designating and defending "strategic interests" all over the globe. It's been a decent 60 year run.
But it doesn't to Afghanistan and Iraq .. mainly because there's nothing to diminish. In fact, looking at those two as independent entities (say "profit centres"), it would be almost the opposite: America has made the investment, abandoning now would be giving up on the cusp of (possibly) accelerated returns.
In other words, I really don't have much to add here.