I don't know if Kate's jewelry is on the "dull" side because she wants to keep the jewels low key. I have the feeling that she is absolutely dying to get her hands on some of the queen's jewels. She'd probably wear a tiara in the shower if she could get her hands on one. Obviously, the queen, who despite the fact that she "adores" Kate, is not coughing up the good stuff!
I don't think so. Mrs. Thriftyjewel got the adorable Nizam of Hyderabad Necklace once, which is 500 grams of pure diamonds - and has hidden it with her sausage curls. She did not even bother to tie the hair back a bit, not to mention a full updo, which would have been more than appropriate to showcase this piece.
So if I were the Queen and would have seen THAT, I would not give her another piece to ruin for a very long time.