The VMC has had this question quite a bit. It's also been popular on riding social media pages.
Yes can go for a drive / ride, but there is a requirement within the actual directives which specifically limit the distance travelled for that exercise/recreation - that the distance travelled must be reasonable. Yes, that is a bit open.
Police are essentially using your postcode as a measuring stick to trigger the infringement unless you have a damn good legal reason to be out further.
Riding to Gembrook for a pie would fail the definition IMHO. You can get a pie closer to home.
Riding to Gembrook to take in the kind of roads you need for mental health has a good chance of having the cop write you up anyway because there may be roads closer. So then you'll be arguing the case with the magistrate if you decide to object - something you are entitled to do.
The virus doesn't move people, people move the virus, so these rules are about limiting movement and interaction. Given that this wave is all about community transmission, I'm inclined to keep close to home.