Yup. Aluminum is too soft.
That part I'm aware of b/c the sensors are generally pretty big if you want that high quality of a camera. Stupid thin race ruining everything.
Z3+/Z4's grille looks best IMO. It kind of blends in w/ the seam between the glass and frame. Here's hoping the Z5 keeps that along with the rounded frame adopted from the Z3 (not that I see no reason it shouldn't). From what I've seen the rounded frame isn't hard to hold at all b/c it has such a big curve radius that it's pretty close to flat. Also I hope they change the back from glass. Matte metal would be good. Same finish as the frame, obviously.
As for the Z2 speaker grilles I feel like it's a lot more noticeable than the Z3+/Z4 because that one cuts into the frame rather than the glass. If you have a frame color that's not black, it seems much more noticeable.