It would be nice to have an option for text shadows (a la Eterm or mrxvt), as this makes it easier to read text when using pseudo-transparent background.
The font rendering is done by VTE, so file a feature request to VTE on bugzilla.gnome.org.
A comment in bug 316005 (http://bugzilla.gnome.org/show_bug.cgi?id=316005) mentions GTK having an "embossed" attribute that can used to a similar effect, and the most recent comment says "Gtk+ HEAD has API to set the emboss color." I'm not sure if this was meant as a resolution to the bug or not, but is this something that could be used for xfce4-terminal?
No, it's just a hint. We need to wait for this to enter VTE before we can use it in Terminal.