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.
Actually, I think you're complicating a very simple idea.
What if I rephrased it, "in life you're going to have to make choices between short-term, feel-good pleasure and long-term, life-improving gain"?
I believe life has what meaning you give it. To Michael Jordan, the 'meaning of life' was to be the best BBall player. To Mozart, it was to the greatest composer. To some, it's just to make it to their next beer.
'Objectivism' is the idea that is is 'moral' for an individual to make the best choice for their 'long-term' interest. Certainly it's *never* possible to fully know which the right choice is. But the main goal of a man (or woman, of course) is to figure out what that is.
It's what we all do, in fact.