I feel like the best rationale for "writing for the audience that is yourself" is to write that which compels you, in order to make sure you're speaking valuably to all those people more or less identical to yourself (which, statistically speaking, in a world so well populated, is a whole lotta people), and to all of the other types of people engaged in meaningful conversation with those people (which is actually a staggeringly large group of people). None of those people (except yourself) may be in the room with you, or perhaps even in your county. But they are most assuredly out there, in serious numbers. And one is much more likely to have deep, richly nuanced layers of meaning and intensity in expression for that audience than they are for the one that happens to be three tables over at the coffee shop.
Also, if you don't write (at least largely) for yourself, then you will likely have forsaken your inner compass, which probably has a great deal to do with why you started writing in the first place. I'm not going to pretend it's the only guide of value (I've heard Yanni doesn't listen to others' music, so as not to pollute the purity of vision), but ignoring it entirely is, in my opinion, a hollow and baffling experience.