Personally, if they are not part of a project then I would not review them in that context.
I might scan through each NA context as part of the weekly review but only if I felt that there might be some open loops. Typically, NA's not tied to projects just sit in the appropriate action context until they are done (due to an intuitive choice as part of a context scan) or until something changes their status to force them into my hard landscape.
One habit that I can't seem to shake and that goes a bit against the GTD methodology is prioritizing my NA's. Staring at and scanning a list of 30 or 40 NA's for @Home is just too big a chunk for me. It was producing a feeling of anxiety. So I prioritize using each priority as a window of time... Priority 1 is for things I want to get to ASAP (this week). Priority 2-4 are things I want to get done SOON (this month perhaps). Priority 5 is for things that I want to be reminded of regularly but have not commited to a specific time frame. Priority 5 NA's blur slightly with the Someday list and often will get moved there if I get tired of seeing them or eventually just deleted outright.
So, for me, prioritizing gave me a little triage and a better sense of control over my NA lists. You might want to give it a try. I find though, over time, that I'm slowly moving closer and closer to the elegant simplicity of the original GTD approach.