Now, regardless of whether I'm talking about self-publishing, the chasing of trends, or the industry in general, there are always going to be exceptions to the "rules" I discuss. (I do my very best to distinguish between "rules" set by industry convention and "rules" I suggest to try to help you out.) Yes, there are self-publishing success stories like Oscar Wilde and William Young (the dude who wrote The Shack). Yes, there are people who write runaway bestsellers by trend-chasing or writing silly mash-ups or publishing a bunch of pictures of cats in stupid outfits. These things, regrettably or not, do happen.
However, they are the (often exceedingly rare) exception(s) that prove the rule(s).
There's an interesting phenomenon I learned about many a year ago while working in a psychology lab at Ye Olde College, and that's confirmation bias. In keeping with psychology/psychiatry's practice of giving fancy names to things everyone already knows, confirmation bias simply refers to the (often unconscious) act of selecting information that confirms theories you already hold. If you are writing a teen vampire romance and believe that it is ultra awesome, you will probably gather information to support that theory, even if the preponderance of data indicates otherwise; this applies to everything from ideas about self-publishing to political and religious beliefs. I'm just as guilty of it as anyone else.
The number of successful authors is, relative to the general population (or even the population of living writers), vanishingly small. The number of successful self-published authors, regardless of how august or prosperous those authors are, is far, far smaller. Just because William Young or Christopher Paolini went on to great success (via traditional methods, by the way) after self-publishing only proves that it is possible, not that it is likely (in the same sense that a lottery ticket earns you the possibility of winning, not the likelihood). This applies to anything in your life that you want to do but for which the shots are long: publish a bestselling teen vampire romance, win a gold medal in the summer Olympics, become CEO of a major company. The odds are longer for some of these than others, and certainly factors beyond luck are involved, but you have to understand that just because someone tremendously talented, hardworking, and/or lucky managed to do it does not mean there is even a decent chance you can do it, too. It just means there's a chance.
Now, I don't mean to discourage you. And to be straight with you, the odds are long in this business whether you write about vampires or alcoholic fathers, whether you self-publish or embrace the traditional agent-querying model. All I can do is try to give you a feel for how those odds change depending on the choices you make, and to encourage you to write the best book you possibly can. You may have to write more than one novel before you're published. You may have to write more than twenty. Whatever you do, stay committed. It's a long road to publication, and there are no shortcuts. There are some paths that are less thorny, though, and with any luck, I'll be at least of some help to you in finding them.