I think the key is staging events the riders want to ride in and the punters want to pay to watch, obvious really and not rocket science. Events like the, I'm going to call it, first division riders championship and pairs where riders are "forced" to ride for a fixed BSPL rate means that riders don't really want to ride in it and therefore come up with any excuse under the sun not to ride in it devaluing the competition which in turn puts the fans off.
Events like the Peter Craven Memorial Trophy held at Belle Vue really seems to have built up some prestige around it. It's run a little differently with a 5 rider semi and 6 rider final, which is truly spectacular, obviously most tracks it's probably not safe to do that but there are a number of different formats that could be run, you've just got to think outside of the box a little bit.