For me...
Pretend no one knows about the sport...
(Won't be too difficult)..
And launch it as if were brand new...
Build a profile for it, make it a brand, get its name out into YouTube etc, with 10 mins behind fhe scenes vlogs, focus on making riders the personalities of the sport, share all merchandise costs and profits using a generic look but with each individual club having their insignia on their version of the merchandise....
Employ people who can influence and hype up the sport to a younger demographic, make websites look like they were designed today not when the internet was invented, use an interactive UK Speedway App, with clubs having their own individual interactive versions...
Stop being so insular, staying sat within a "Speedway Bubble Echo Chamber" and instead open yourself up and bring in people much younger from outside the sport (if the skill set doesnt exist within it already), who can bring fresh ideas that white, middle aged men wouldn't even consider...
Put the fans' "match night experience" front, back and centre of everything you do...
In short.
Look at what successful sports do and use as many of their ideas as is possible to help grow Speedway..
But, most of all, run it on the bloody nights that your fans find are the best ones for them to attend with their kids!!!
And also find a way to get a fair few dozen away fans in attendance to add some bloody atmosphere!!!