This one had me scratching my head for a few hours today. I was trying to plot several sheets of cross sections but no matter what I did, Civil 3D put huge spaces between the section views enabling only a handful of sections on each sheet.
I monkeyed with the group plot style over and over until I was just about ready to give up. Turns out, I had a band that was taking up a lot of space due to the band height and text box width settings (highlighted to the right).
Once I set these values to something reasonable, all of my section sheet problems went away.
File this one in the back of your mind somewhere in case you ever run into something similar. This can come in handy, by the way, when you need to make space above or below a section view. For example, when using Plan Production (this works for profiles too) you might need to create some space above or below the view so that the viewport is large enough to fit labels and doesn't cut them off.