In IDEs such as RStudio and Eclipse, there are global options for users to set how the code editors should look (e.g. font size, tab width, auto intent etc.). Having such an option for the custom expression and data function editor in Spotfire makes it more developer friendly. Especially in the case of font size, it's very useful for those of us with bad eyesight.
Agree, it would be useful to be able to quickly magnify the font (say when giving demos) or to shrink the font (when examining some code)