How to simulate sculpt layers in Blender? I'm wondering if there is a way to sculpt some details on top of existing, already sculpted details, and then change the opacity of newly sculpted details? For example skin pores on top of a wrinkles geometry.

It's like working with layers, where you put a layer on top of the layer underneath and then set the opacity individually for each layer. This apporach is used eg. in Mudbox, please take a look at the following tutorial on 8:20 mark:

https://youtu.be/fh0mZcblVJ4?t=503

Does Blender support that approach or is there a clever way to simulate it?
You may be able to use the Sculpt settings in the Multires Motifier in that way. I generally just do all my sculpts on one layer but setting up multiples in this way may do the trick. Hope this helps.