When any material, no matter what it is, touches another different material it generates an electrostatic charge. See the triboelectric series for more on this. For plastics there is going to be charge generation, but it will be negligible and so I wouldn't be worried about it.
If your circuitry is extremely sensitive to electrostatic charge then I would design in some kind of electrostatic shielding separate from the case itself. Or you could use a conductive paint on the inside of the case, which causes the field lines of the electrostatic charges to say on the outside of the case due to the Faraday cage effect.
One question I've been wondering about related to your question is the conductivity of the alumide, black polyamide, black fine detail and the black color of the full color sandstone. If any of these were conductive at high voltage levels then they could be use in electrostatic devices. I've been meaning to order a sample of each of these so that I can do some tests to see what is possible.
I prefer to know nothing about everything rather than everything about nothing.