It is not 'happiness' that is Rand's highest good.
(Forgive me for repeating this *yet* again, but . . .)
Consider the man who is happiest eating cake for breakfast, lunch and dinner. He is acting *against* his own self interest and long-term happiness (destroying his health).
I'm really surprised, how can such a simple thing be so widely misunderstood?
But this still reduces happiness to the having of certain sensations. What about Aristotle's statement in the Nicomachean Ethics that "we cannot call a man happy until he is dead?"
Either there is a goal or purpose to human life that lies behind "self-interest" or there isn't. If there is such a goal, then wouldn't the pursuit of that goal be the purpose of life, rather than just self-interest. If there isn't such a goal or purpose, then the pursuit of self-interest may well be our highest goal, but that doesn't tell us much about what we should do. So what is one's "self-interest," and how much freedom is there to disagree about just what one's true self-interest may be?
Alternatively, there may be no one purpose or goal or standard of value. I may resist attempts to force me to make sacrifices for some presumed common good, yet still praise those who, at critical moments in history, have made just such sacrifices. Self-sacrifice shouldn't be made the end of our existence, but civilization owes much to those who sacrificed their lives for it. I don't think Rand would disagree with this, though she might try to fudge things to preserve her slogans.