Perhaps part of the problem is our desire to bundle solutions into grand theories, like supply-side economics or Marxism? I agree that we can beat a horse over and over again until there's nothing left to see, but small changes are how the world actually works. I can say "lowering taxes on producers of x can stimulate growth" or "increased public investment in industry y will resolve the problems it currently experiences" and those things occur all the time. But they also don't sell books.

EDIT: Perhaps a better way of stating this is our desire to package academically useful economic models into grand policy solutions.