As you may already be well aware, and apologies if so, engineering officers in the RAAF (and in similar roles in the other two services) are far more at the man management end of the spectrum rather than actually working on aircraft. The vibe I get from your post is that you're thinking of getting your hands dirty rather than supervising those who do, is that right?
Anyhow, the squadron ENGO job is basically about organising and reporting on the maintenance system, being the liaison between the workshop and the rest of the organisation etc. SNCOs do the hangar floor supervisor job and some of the spanner swinging, then CPL and below do most of the hands on stuff.
Aeronautical engineers at places like ARDU could expect to do some real engineering, eg designing mods and so on, but as I say, your squadron ENGO doesn't do a lot of real engineering.
a future life as an engineer as a civilian post-military
If by this you mean LAME qualifications, you'd need the hands on experience, ie the other ranks path. Serving as an SSO would set you up with some management experience for the resume but not the technical quals.
I worked as a breaker rather than a fixer, so apologies for any rash generalisations, but my mates who were ENGOs certainly often bemoaned the fact that they spent all their time signing leave apps and doing paperwork rather than putting their uni qualifications to use.