I read this debate with interest.
I followed Peterborough home and away from the seventies to the noughties but stopped going over a decade ago. The last meeting I went to was a World Team Cup qualifier won by a professional Polish side against a set of English strugglers (amongst others)
Main reasons I stopped going:
Too many guest riders - got silly when your main opponent's in the league No1 was consistently your highest scorer
Team makeup being destroyed by a calculator-fuelled rulebook. Too many races where one or two riders were left at the back race after race.
Poor relationship between riders and fans - too many riders straight into their vans and off to the continent after a meeting, instead of mingling in the bar.
Anonymous riders/promoters - no real atmosphere especially during local derbies.
Long drawn-out interval before the last heat when 4 times out of five you knew who would be riding. This became especially annoying when I moved a two-hour drive away from the Showground.
And I also believe the axing of the junior races/rider of the night/junior league matches was a mistake. It might not have had all the spectators there, but you could start to identify the gems as they emerged.
On it's day, or preferably under the lights at night, not a lot can beat speedway. It just needs to be tightened up.