Very interesting post overall, but this was the paragraph that stood out to me, because Madame Secretary has become one of two shows I'll consistently watch (The Good Wife being the other; Castle lost me the last couple of years with jerking the couple around). One, I love watching Tea Leoni in that role, and two, I love watching the relationship with her husband, even if the fact they're trying to turn him into SpyDaddy is annoying. But that show has been proof to me that married couples can be still interesting and spicy, as Stana used to say. I kept hoping that they'd find a way to balance the COTW with a funny, healthy, spicy marriage relationship between Castle and Beckett.
Would you add Julianna Margulies to your list of brunette female actresses who get work? Though I realize she's a bit older than the others you mentioned, but The Good Wife had some excellent writing/acting and that fifth season, in particular, was just awesome.
I probably won't be able to bring myself to watch the last few episodes of Castle. I don't want the end to poison the first three seasons for me.