I'm no steady expert in the slightest, but have done some extensive research recently as I'm looking into them myself. According to my recent google-fu-ing, if flying a lightweight camera, a vest it will likely get you worse results than using a stabilzer on it's own.
Just as a longer stabilizer isn't always best (as you end up with relatively too little weight on the ends, and thus center of mass is closer to the fulcrum), the vests function better with heavier loads (too light a setup will not allow the arms to function as well).
Basically the heavier the rig, the increased need to go up in size, and then a vest cos yer rig is so bloody heavy. Thanks to all that mass and leverage, a larger steady and a vest will be capable of a more stable shot, but only if the mass is there to make the physics add up in the first place.
If you've got a stabiliser already, then learning how to set it up properly, adding more mass, getting the gimbal as central as possible, practicing your stalky/shuffly walking, and more flight hours will yield better results.
To the best of my research anyway, it is indeed a balancing act (if you'll forgive the pun). So unless you're lugging around a tank-like rig, I think you'd be better off spending your dosh on some pimp glass (and a camera to slap it on), but even more so.... some audio gear of course.