Dreaming I saved the human race?

Yes.

If I can't tell the difference, I don't know how this applies. At that point, we're back at solipsism. If my experiences are false, then any attempt to steer my future is doomed.

Any attempt to experiment is doomed. You have to make a decision under uncertainty. You'd have to do that anyway. It's just that now "experiment" isn't one of the options.