Wondering if there are any obvious signs that the AU ABS sensors are buggered?

generally no,
some visual things that can cause a fault light, broken wire or dirty plug connection, the one ive seen the most is metal shavings sticking to the sensor interfearing with the signal..

The ABS in my ute is working fine to my knowledge. The ABS light doesn't stay on. I was more curious than anything just in case problems should arise sometime down the track.
Is it easy to clean the sensors?

Next time you have the wheels off, pull the rotors off too and give the sensors a wipe with solvent or a spray with Brakleen. Give the tone rings on the rotors a good wipe while you're at it.

The rear ABS sensors do a 90-degree turn through the backing plate and are very easy to break (at least on the sedan); so avoid removing them unless absolutely necessary.