The Axis Forums have great What IF sections that have dealt with this question.
Australia was just too far and too empty for much. The Japanese only were in the DEI for the oil. There was nothing they really wanted there except that. Australia was tiny in terms of population. Only Melbourne and Sydney were worth anything really. There was a few “lines of defense” drawn up by Australia. Usually from Brisbane to Adelaide and everything south of that. Though there were more plans than just that.
It was the same thing for Japan and Siberia. They had no use to go where there was nothing they could use ASAP. Sure Siberia was rich in resources but getting them out would’ve been hard enough during peace, it would’ve been a nightmare during war. The Japanese were still developing Hokkaido in the 30s and very slowly expanding to South Sahkalin
But attacking Aussie was not out of the question as one of the war aims seems to have been grab as much as possible as fast as possible and then negotiate peace with the Allies once they were tired from fighting Germany.
Australia had a lot but it was far, the urban areas were sparse, the means of transporting resources, like roads and railroads were easily subject to sabotage (If you have one railroad line going out west, it’s easy to cut it, rendering it useless for the invaders)
Any resources they could get from Australia they could get elsewhere where they were already fighting or in control. So while invading Australia would have shock value it wouldn’t be much help.