I suspect the rendering of the table is more down to the mail client you use and how it chooses to render unstyled tables.
You could maybe look at doing some XML manipulation to add some inline styling to the HTML table that is generated.
If you could give an idea of what you want the table to look like if I find some time I can look at adding some pre-defined styles or custom styling options to the node.
I assume you are talking about things like border, background etc rather than number formatting?
Cheers
Sam