I'm gonna circle back to an earlier point: SCCA-Sports Car Club of America is a model the shooting community should examine. Very similar issues with gear races, developing skills and staying relevant. The old school divisions like Formula Ford and others are still there for the big money folks and are as popular as ever. There are also divisions which have come out relativity recently like spec Miata which is a massive division using you guessed it, a Miata built to certain specs. There is no cheap racing, the best PRS rig is still thousands less than pretty much any competitive racer and prep is even worse. But racing thrives because there's something for everyone-kinda like nrl22, 223/308 divisions etc. Oh and if you want more movement, the racing parallel is endurance racing. Most racers can't afford the fun tickets to go 6-8-12 or 24 hours, but some do. You could have matches that have increasing levels of activity to accommodate folks whose knees and back aren't shot to shit.
Vintage class could be a thing as well.
IPSC/USPSA went through almost exactly this same evolution I'm seeing here.
USPSA has a system to tier shooters based on demonstrated ability. They chose to use a set of standard stages called classifiers.
But there are several other ways to segregate shooters into ability tiers without having standard classifiers. Sporting clays, both here and in the UK, have zero standard courses of fire. Every club is different, and the course will be different one month from now even in the same club. Yet both have shooter classification systems. One based on percentiles the other based on points accumulated based on in-class finishing position.
USPSA has a system to separate equipment into different divisions based on characteristics and features, not product cost. It has divisions where you can spend $4 - 7K on a custom pistol and divisions where you can spend $500 on something off the shelf at the LGS and not be handicapped.
USPSA has a rulebook that gives consistency to safety rules, match administration, arbitration, scoring, and several other issues while giving local match directors significant latitude in designing stages and running matches.
There's a lot to be learned from other shooting sports while adapting what one learns to suit the differences between those other sports and a rifle match in wide open natural terrain. Think concepts and principles, not details.
Most of the solutions are already out there. It only takes having a mind open to learning.
I also think whoever said "define first what is to be tested" is right on point. A match is a test. Define that, and structuring the rest around it becomes much easier and clearer.