You seem over-worried to me. Your experience is relevant in all cases.
Your background is solid enough to get back on tracks and reach a permanent position. The only thing that matters now is, as Richard U said :
- Network, network, network, and then network some more. Talk to friends, family, acquaintances. Tell everyone you know that you want to get back to doing full time work.
Networking is the key to reach a goal, tell people about it and let the noise make its own path. People will hear about you soon enough and be either interested and/or intrigued by you. You are a senior in several relevant fields, which may make you over-qualified for some positions.
However, by explicitly stating what position you want (I assume IT department), you will ease the process of your comeback.
Here are some steps I would recommend :
Keep doing that, never stop
- Update your resume to match the position you want. Make it shiny and fashion.
If your struggling to fit all in, remove/lower importance (for) irrelevant experiences
- Upload your resume on some social networking platform (once again, not a crappy but relevant one)
You can specify here everything you've done, don't limit yourself to IT position, write it all
- Train yourself on new techs, methods, processes, ...
Keep doing that too, never stop either
- Apply to positions
- Don't let applications go unseen / forgotten
Keep reminding HR (be reasonable, avoid harassment) that you're interested until you reach an interview
DO NOT LET GO OFF THE PHONE WITHOUT AN INTERVIEW
That is extremely important
I don't need to explain why
Networking is so important, it has already been explained greatly by Richard U.
3 is important to gain visibility and activity, HR WILL see you there and you will see them. That's related to
4 on the other hand is based on pure assumption as your IT background may have become "outdated" for some positions. You are a senior developer, but your methods and languages may have been deprecated, enhance and renew your skills !
This will show several important factors about you, such as being able to adapt to new technologies (Fork some projects on Github, code and contribute to some others for fun, learn to enjoy it all over again).
It feels like most recruiters want to see recent experience in a relevant field, which I don't exactly have
I don't think that it's true. IMHO, recruiters will apply such process to juniors, not to someone with such a heavy and adaptive background as yours. If so, an up-to-date Github portfolio will do the trick.
and their rigid application forms/processes are not well designed for unusual backgrounds like mine
Then contact them directly without passing by such form. If they still want you to apply this way, do it, but not without letting HR know about you prior to that. You have to pop into their heads enough that whenever they see your name they go "Oh, this is that guy again".
And slowly but surely "That guy again" will reach their thoughts enough to accept an interview with them.
Do not be afraid to ask for one, you have the right to do so, don't wait for them to make the moves !
So far, I've had zero responses (not even acknowledgements) from the posts for which I've applied.
You should go and get those responses, waiting just allows HR to forget about you.
Hello, I am inquiring about my application to X position submitted on dd/mm/yyyy to which I didn't have an answer yet [...]
[...] but I believe could nevertheless be very valuable to them
That's the spirit. Play on that and keep believing in it, if you believe it enough, HR will be convinced and see your potential rather than your recent experiences.