The column widths are currently based on the widest their content is generally expected to get. For example, the length column is the width of "0:00:00 ". In that example, the space is only 1/8th of the width (with a monospaced font), so I don't think custom spacing would make much difference to your issue. I will look into calculating the width of the length column dynamically based on the playlist content, eg. don't include the hour column if all tracks are under an hour long.
Btw, I was mistaken above regarding the WTF skin's normal font for that text. It's Tahoma (not Arial), set in the skinconfig "font_listnum" entry.