I wouldn't worry about that number as much yet, since we're almost a third of the way through the initial period. If we can make the downward trend of visits/day level off, then the questions/day should take care of itself. I've already seen a lot of new users this week, here's to hoping they stick around.
If you look at the full site list, Japanese has more questions/day than the newer betas, with the exception of Gardening (which is a week newer and has less visits/day, so that question average will probably decrease in the next week). So the relative performance against sites open for just as long is pretty good. Even the performance against some of the older betas is pretty good.
We've also got a very active user base among the power users we do have. Our meta is pretty active and we're still getting questions with really good answers like this one.