Yes, I hadn't really thought about Titty for various reasons, even though she's so charming - she's certainly a little more sensitive than either of them (witness the dowsing episode in PP) and she gets a really unique perspective and usefulness derived from that. (Again, like the dowsing!)

Absolutely, to your last point. A commenter above offered the comparison between Nancy and Susan, and George and Annie from the Famous Five books, who really fit the stereotypes you're pointing out (and yet George still takes orders from Julian and Dick, and Annie's work is never valued.)