Fernando Alves points out that iTunes 11 does have a means of increasing the font size. To increase the font size used in lists, check the “Use Large Text for List Views” option.
Note that there is only one large text font and the standard font, there is no fine control of font or font size. This option also only changes the font size of the list-oriented screens (Songs, Playlists) and not the other display options (Genres, Artists, Albums).
Using the alternative font doesn’t really change the row height in these tables, so the end result seems a little crowded, but at least the text is bigger.