If I spend a decade getting qualifications in psychology (driven to the field because the science interests me and is core to my way of thinking), what are my career options?
I wouldn't be against practice with the mentally disabled, but what other things are out there for psychologists?
First of all, it doesn't take a decade, it takes 6-8 years to become a registered clinical psychologist. 3 Years undergrad, Honours year of running an experiment, two years of a masters (there's a couple of different ways you can do some of those, but in your undergrad, you have to do an accredited psych course).
If you decide you don't want to go into clinical, there's a whole heap of other areas like research, human resources, recruitment, government and policy, many psych majors combine it with marketing and go into advertising, etc.
If you decide you want to go into research or clinical, there's also a heap of different areas of psychology, some of which you can see here
http://www.psychology.org.au/studentHQ/careers-in-psychology/
The Australian Psychology Society is really your best website for figuring stuff out.