Using Modelsim/Questasim 10.6b with a 4K monitor makes it difficult to see the lines for signals, especially std_logic signals, vectors are a little better.
I was able to increase text size via edit->preferences but haven't found anything similar for wave "weight" or "thickness".
Not a 4K monitor user, but have you tried modifying settings at Tools -> Edit preferences -> "By Name" tab and looking for wave?
I've just figured out that going to Tools -> Edit preferences -> On fonts section look for "waveFont", i can increase waveform size font. Which, by default, is tahoma 8