These aren't suggestions as I realise implementing them would take a while (GObject; **** yeah! [Though, props to Vala - implementing properties and D-Bus methods and signals is so simple in Vala that it's almost orgasmic...), but ideas of what can be done with D-Bus if you ever feel like extending your brilliant efforts.

* If your object uses GObject properties for settings etc., you can manipulate them with the standard org.freedesktop.properties (something like that interface) as DBus-GLib will export them. You've already provided get/set_param methods
* You can also allow signals to emitted - create them in the GObject Way and define them in your interface XML. You could have one emitted for when a widget is updated.