Something for the dark top areas of your pages:
Start by applying filter smart blur. It doesn't actually make your text more clear, but reduces the graininess of the unwanted noise by combining the particles. Play with the settings:

As said, the smart blur step can be skipped, but there will be more fine grain in the end.
Duplicate the layer. Apply heavy Gaussian Blur to your top layer to fade text details:

Invert the top layer (Image > Adjustments > Invert) and change its blending mode to Linear Dodge or Add:

Insert a curves adjustment layer and lift the contrast with it.

NOTE: The curve should be as mild as possible; vertical tresholding doesn't work, it makes the letters much rougher.
Approximately the same can be got a little faster with high pass filtering. Start by smoothing fine grains with Smart Blur as in the first receipe. Then fade large uniform dark areas by applying High Pass filter:

Restore the contrast with curves. Again: vertical tresholding will not work, the curve must be as mild as possible.

A mathematician might be able to prove that the methods are same in math. A valid proof needs underhood qualitative knowledge of Photoshop's functions. Adobe has kept those details well hidden.
NOT ASKED: If this was my job I would recreate the pages from scratch for ex. in Adobe Indesign, only signatures must be copied.