If you buy a day ticket for the main racing only, its £28 (or £34 on the gate). That's not quite so good.
You're right, though - just because something isn't comparatively expensive doesn't mean it is value for money and, in many cases, speedway does fall down there.
I went to the Belle Vue/Wolverhampton TV match last season and, basically, everything was just bang on. A reasonably close result, some fantastic racing, an Aces win - we even had Chase the Ace doing a 'Staying Alive' dance. I paid £10 but even at the usual £17 it would easily have been worth every penny.
All too often, though, we have crap tracks, ridiculous, unnecessary delays, poor presentation and riders who can't be bothered. All that has to be addressed, and soon.