tAlso the cast is freaking HUGE, and for plot purposes that's awesome, but it's hard to pull that off without under-developing relationships and character growth.

*nodding too*

Actually I remember feeling this way during BSG 3.5 when the development of more and more b-level characters was kind of disrupting the arcs of the storyline as a whole and particularly the arcs of the more central/original characters. It's a logical progression for casts to grow larger as a show goes on, but it sucks when that happens at the expense of the plot's tightness!