I get that money is a factor in casting TV shows, but I think there are good reasons to limit a cast that have nothing to do with money. The larger the ensemble, the more diffuse the focus, and worst case scenario, you end up with a situation like The Next Generation, where it felt to me like the writers were playing round robin getting everyone from the cast involved, regardless of which character was best for a story or which story was best for a show.
Some people complain that the focus shifted to a few of the characters in the later seasons of Voyager. I loved it. It gave the show more structure and definition, with three clear leads (Janeway, Seven, doctor), two major supporting characters (B'Elanna and Tom), and a handful of minor characters (Neelix, Chakotay, Tuvok, Harry, not to mention Naomi and the Borg kids, who brought a lot to Seven and Neelix's character development--I'd take Naomi, Icheb and even Mezoti any day over Kes--in fact, I think those characters brought to the show exactly what Kes was meant to bring but failed to bring). And I'm not just saying I loved the direction of the show because it favored my personal favorite characters. My favorite character in the Star Trek franchise is B'Elanna, and I like Neelix just as much as I like Janeway and the doctor, more than I like Seven.
As for who to let go, in order to make a manageable cast, I agree with the writers' statements that they'd run into a wall with Kes' character--wrote themselves into a hole is what I'd say, by abandoning the initial concept of a child character and turning Kes into a superbeing. Omnipotent characters are harmful enough to plot and consequence when they pop up occasionally like Q. They certainly shouldn't be part of the main cast.
