Hmm, this will come off as a very broad comment, but in general I don't see further education to be an advantage for finding work, especially when you think of the money you'd dump into another degree and spend more time out of the job field. You'd probably have better luck in low level municipal planning jobs that you are over educated for and use extra years you would otherwise spend in another degree working your way up.

I took a construction coordinator job that I know I'm over educated for, however I've learned so much in the two years I've been here, earned an income, and know I'm further ahead than if I just spent the time getting a construction management degree.

Just my opinion, I'm not a huge fan of spending more years in school, especially after an M.Arch.

I think an Urban planning focus would be a good adjunct to my Architectural education and wouldn't place me at a disadvantage when returning to Australia. The alternative was a PhD, which is much more work & time (when I return I'd like to return to practice)

I should hope additional education wouldn't place you "at a disadvantage", but if that's the best you can say for it maybe it's not a good idea.  I agree with chris-chitect above.  Grad school is an awfully expensive way to hide out from unemployment/underemployment.