I'm gonna go ahead and split the difference between opinions.
The test is all about time management, just like any test (ASTB, SAT, etc.). So, with that being said, the math and reading comprehension parts shouldn't be something you really have to study for. I hadn't done basic math/algebra/geometry in for-fvcking-ever, and they made me take a practice ASTB the other day (hooray being a guinea pig for NASC) without telling me. I sure as hell didn't rock it, but I scored a standard deviation above. If math or reading comp aren't your strong suit, though, it wouldn't kill you to *brush up*.
As for the general aviation knowledge, I wish I'd known more about it. I did pretty well, but my weakest points were the specific FARs and ADF/VOR questions (completely foreign to me). Same thing can be said for the spatial orientation portions. I would highly recommend looking at it before hand just to get familiar with what's expected of you. It'd be a shame to waste 5 minutes trying to figure out a system for deciphering what the hell is going on.
TL;DR - It is an aptitude test, meaning you don't necessarily have to study for it. However, I don't know how anyone would come of the street knowing what ADF/VORs or specific FARs are without some prior study time. Bottom line - go over things, but don't nuke it. A few hours in a book or online will help, but it won't necessarily guarantee you to pass.