Importance of Math Subject GRE
I think the simple answer here is that (a) it depends and (b) the entire application "package" is considered when admission decisions are made.

What I mean when I say that it "depends" is that it depends on where you are applying. If you are applying to a top math program then there will be many many individuals applying for admission. Of these, a subset will also likely have publications and will also likely have high GRE scores. I say "likely" because it's impossible to know the strength of the applicants in any given admissions cycle.

What I mean when I say "entire application package" is that, in some respects, you can make up for one lacking area by excelling in another; take this with a grain of salt however. You are applying for admission into a PhD program. The important question the admissions committee is trying to ask for each applicant is "Is this individual likely to succeed in doing research in this department?". Past publications speak to this much more directly than do GRE scores. Classroom performance is no longer the emphasizing factor -- it's all about the research!

As others pointed out, if you have a faculty letter of recommendation that supports your contribution to the publications you have that will be huge! If not, the admissions committee may certainly wonder what your role in these were, particularly if you are not the first author.

Additionally, top PhD programs may use GRE scores to "weed out" some initial applications. Nobody has time to go over the complete admissions package of 500+ applicants.

My advise: if you have time, spend another month or two doing some extra GRE prep and retake the test. It sounds like you have a strong application other than the one score. Spend your time only studying for the math portion. Some programs will let you "pick and choose" which scores of which test to submit (i.e., submit math from "test #2", submit vocab from "test #1", submit writing from "test #2"). At any rate, because you are applying to math departments, the math score is really what matters!

Hope this helps and good luck!

Edit and disclaimer: My background and experience is in applied math and computer science fields. As another poster pointed out this may be different for pure math department applications.