if I were you I would change the site structure and apply following
organisation.org.au/center1
organisation.org.au/center2
organisation.org.au/center3
would redirect old subdomains to sub-folders with 301.
This has been discussed several time, even Rand has a white board friday for this.
Lastly, yes it's worth moving subdomains into sub-folders, you will notice ranking increase by doing so 
