[JustForFun]

@kovid
This was not really the answer I wanted to hear, but unlike most other calibre users I'm indeed able to change the source. Would you accept the attached patch for one of the next releases?

The attached patch introduces the new tweak "change_book_details_font_size_by" which let the user specify the increase or decrease of the font size in the book details panel and the comments editor in the metadata dialog. The default value is 1 (pixel) to be compatible with the current version. Users which prefer the old behavior can set this tweak to 0 so that the font of the book details should be the same size as the default UI font.
(Hmm, reading this paragraph again I wonder if the tweak shouldn't better be named "increase_book_details_font_size_by".)

The patch was generated with "bzr send -o ..." as described in the user manual.

Off topic: Congratulations and my best wishes to you and your family.