Slaw -
With regard to the aluminium plate/acrylic. I would not run the plate, it's added resonance. I have moved away from metal spikes, and if I use them I radius the tip so it is not a sharp point. I say radius, as in rounded, NOT flat. The idea is a small radius tip sitting in a larger radius hole as per most unipivot bearings. My suggestion would be to radius the tip of the grubs screws and then you should be able to couple directly to the acrylic without damaging the surface. In an ideal world the acrylic would have a dimple in it for the radius tip to sit in.
With regard to the aluminium plate/acrylic. I would not run the plate, it's added resonance. I have moved away from metal spikes, and if I use them I radius the tip so it is not a sharp point. I say radius, as in rounded, NOT flat. The idea is a small radius tip sitting in a larger radius hole as per most unipivot bearings. My suggestion would be to radius the tip of the grubs screws and then you should be able to couple directly to the acrylic without damaging the surface. In an ideal world the acrylic would have a dimple in it for the radius tip to sit in.