From what I understand, it really isn't all that important, and is only used [in most departments] as a secondary or tertiary score, and sometimes in consideration for requirements for Fellowships and the like. I see plenty of [self-reported] perfect scores and perfect GPAs on here, yet many of them received rejections. Goes to show that even with top scores, there are other things far more important. If I had to take a guess, I'd bet it's a combination of 1. conference/publication/research track record, 2. writing sample, and 3. letters, not necessarily in that order.
For the record, I too was very worried about my GRE scores. I'm a bit "later in life" and hadn't had a math class in somewhere around 14 years, and math was never my strong suit, with my highest college-level math class being regular ole Algebra I. But thanks to that 5 lb book of GRE questions, which showed the methodology behind the solution of each question, I was able to find some patterns and memorize basic equations. I was happy enough that I scored a 153 quant (51st%) and called it a day.
Similarly, I too was a bit confused that departments don't care more about the AW since it seems, in my opinion, to be the thing most applicable to philosophy (with a close second being verbal reasoning). But I think many departments see that a writing sample is far more indicative of an applicant's philosophical ability to understand an issue or problem, construct a solution, argue for it well, recognize and dispel objections, and do all of that in a way that's clearly organized. That's my suspicion, at least.