Ta - perhaps it's me... Or something happened during the mot...!! I doubt they'd done many before mine (and I expect that's where the mirror was broken).
I have exactly the same feeling as yours regarding vibrations. But it's quite understandable. When something is more rigid, it transmits vibrations more easily.
I have been waiting 2 months for my dealer to get some stock of brackets, apparently there are 2 different varieties. All brackets do not fit all cars.
I expect things will fall off even more quickly now due to the increased vibration, but sounds foolish to moan about another one step forward two steps back improvement!
Fingers crossed there's plenty of Loctite on the beastie!!