Crude simulations may or may not invalidate theories, but they're notoriously bad at weeding out ultimately inviable lines of investigation. The raw, real world is messy and unpredictable in a way a simulation can never be, and until something from the DARPA Challenge or its ilk can handle meatspace, we got no business trusting meat with it.

Not to say simulations are bad things; they're just of limited utility. Beyond that point, it does get expensive. I think that's part of the reason for the Challenge in the first place.