Regardless of the pitcher's material, I recently learned something: picking your next scene at random is pretty goddamn stupid. Like, Santa Claus Conquers the Martians stupid. I did manage to make that set of vignettes work, but to be honest, I think I got lucky.
When you have a large ensemble cast like this, it's easy to lose track of them. I think I mentioned in a previous post that I write down all the pages that each of these key characters appear in, keeping an eye on how long it's been since a reader has spent time with any one in particular. If you're doing this, good for you.
So you finish a chapter and are scratching your head wondering who to turn to next. List out all of your viewpoint characters. Mark next to the names the following information: whether they appeared in the most recent chapter or the one before (don't worry if you haven't seen them for more than two chapters, I'll get to that in a bit), the most recent page number in which they were the vignette subject and the number of pages that have gone by from their last vignette to the end of the story you're at right now, as well as the number of vignettes they've so far hosted.
Now you do process of elimination. The characters who just appeared in the most recent chapter, ditch them for the next one. Just give them some time off and let them breath for a while. And if they've been in each of the last two chapters, then DEFINITELY leave them alone for a while. You have other characters in your story, don't neglect them.
The characters that have made that first cut, go through them and check the ones with the fewest number of vignettes to their names. Chances are it's been about a hundred pages since you've let the reader spend time with them. If they've had only a couple of vignettes, then this is prime time to right a new one that gives them more character development.
The point of this little exercise is to figure out which handful of main characters have been sitting on the bench for too damn long.