Yeah, I'd seen that thread. Unfortunately it doesn't seem to go anywhere and the original poster's website makes no mention of Vala at all.

My attempts to get Monodevelop working seem to have stalled: it's all compiled, but fails to startup properly:

There's an Eclipse plugin for Vala, called Valable which has basic syntax highlighting, but doesn't seem to have had any commits recently. Got it running, but there's nothing it gives over Gedit at the moment.