you are correct, spiral not required normally (perhaps in private specs). It will not affect nadcap audit frequency but will certainly improve media for more assurance of passing audit. For air-blast equipment with just a few nozzles all of the media could go through sprial but the flow capacity is limited. See the new Profile Industries sprial. They do something very cleaver. They rotate the spiral thus improving on thru-put.

Profile Industries Spiral Separators