Ayn Rand doesn't work because her philosophy argues that what can't be perceived doesn't exist. Thus, her philosophy discards the existence of God because he can't be scientifically perceived (the religious would argue that he can be perceived.) 1,000 years ago we couldn't detect atoms, far-away planets, or the like - it would now seem silly to argue that they don't exist. But, apply Rand's philosophy to those times, and her followers would claim that they ~couldn't~ exist.

Thus, either
a) Objectivism is flawed or
b) Objectivism thinks we know everything already.