So my guess is your key skill that so many very good engineers lack is the ability for you to work with the business, understand the business needs and translate that into technical product vision and priorities. This set of skills are very underrated in most small companies and startups overall, yet it is the one thing that can really have a solid and positive impact on all companies. In my opinion if you want to move back into a tech based company and out of financial services you should focus on those skills as your sales point. Your tech skills could be less than others, but if you can turn business needs into tech vision and priorities that is more valuable.
Not sure what the Sydney or other markets you mentioned are like, so your mileage may vary.
You could also look at product roles, e.g. where you are a product manager or something similar. Again since you want to be hands on technical you'd have to do this in a smaller company or startup where you could do so.
As for my experience, it wasn't that difficult to do. I just sought out positions which seemed to gel well with my experience and desires. Honestly, when I joined the current startup I am at, I joined as a Senior Firmware Engineer. I am doing more now that uses more of my total experience, but that was how I joined and I loved it cause I initially really wanted to spend some time just in code.
Last year I switched from ops manager/factotum in a small agency to a pure dev role in a corp. I get to think about technical stuff most of the time now and it feels okay, despite my fears about the 9-5. Thing is, it took me two years to get to that point. I knew I wanted to move for similar reasons to those you list. And Imagined that I had to head for a job that would value my agency experience which was varied and had a management and client-facing bias. So I felt like I was trapped doing the same sort of stuff. I was good at it, but it wasn't making me happy any more.
I have a technical background (programming language theory) but it felt so long ago as to be irrelevant. And perhaps it was. I managed to get second interviews for engineering roles -- which is what I wanted and I turned a couple down because they weren't quite right.
Then this happened. Back 2 years ago, when I started to look for a change, I also got excited about some new-ish tech (Elm, in this case). I started running a local meetup and going to relevant conferences just to scratch my itch. I got a three month contract using it and took unpaid leave from the agency to give myself the chance to do it. But as soon as I added it to my CV I got a call from a recruiter from a local company who wanted exactly that tech. Now I work there and they sponsor the meetup that I still run.
I admit I hit it lucky in this case with a genuine excitement for an emerging tech, and a local employer who were early adopters. But I think the important thing is that I was doing this alongside job hunting and hadn't even connected the two. I was finding a way to do what excited me, and being committed and passionate about that. Then when the chance came up, making the move was easy and pleasant.