Oregon and Seattle used to each run every other month, about 5-6 events per year apiece. That made about 1 event per month if you were going to both (which I highly recommend, if you've only played in one chapter, you haven't really played "Nero", you're playing one plot team's version). That was back when both chapters had smaller player bases though (and larger plot teams (or much, much smaller ones like just me and Jeff, or me and Mark), and no budget, at crappy sites, and no npcs, and... well, I think fewer events is better.)
In hindsight, I recognise a lot of things that could have been done better, but that was before I had all the experience that I have now, and back then, it was all fun because it was nero, and I was new enough that that was all that mattered.
If a game was going to run too frequently, I think that it might be benificial to the plot team to have another group run an event from time to time, rather then cycle plot people off once a year so they can PC. I never liked the idea of PCing in the chapter I was running plot in, just because I knew that I couldn't get involved in the big plot lines for very long (like, those two days I suppose) and you couldn't really have an impact. I think a separate group running one event a year that all of plot could get in on might be better, that way it gives everybody a break at the same time, and no one who usually pcs and has specific plot loses it when that plot member is on break.
Right now, it's looking like no nero events until April, and then there's the May one, and after that I don't know what's up. So, two months off, two on, then what?