Changing scale of working area I want to squeeze NLA editor and Dope Sheet on Y axis to fit more objects in one screen.

For example in VSE this can be done via CTRL + MMB and dragging in prefered direction. Same thing in NLA only works for X axis or stretching timeline. In Graph Editor it works in both ways, but doesn't affect list of objects, so still lots of scrolling.

Another thing I tried, was pressing NumPad's - while hovering over the interface. In some parts of it font resizes well (like Render or Object tab), but not in NLA - it just hides all rollouts.
If you want the Y Axis to be smaller you need to make the Text/Font smaller.

You could reduce the Display Scale under the User Preferences > Interface.



However, this will affect all unsizable text in Blender.