Not sure about Belle Vue but the figures published are as follows:
Warsaw 48k , Vojens 19.90k , Wroclaw 13.50k, Torun (SoN & SoN2) 13.10k, Gorzow 12.50k, Prague 11.50k (inc SGP3), Manchester 11.50, Melilla 8.70k, Landshut 7.8k and Riga (inc SGP 2) 6.70k
Appreciate what you say about the venues but it does seem that live attendances might be in decline and that is not good news if the plans were to spread it around other non European stadia. Maybe fans are tired of the format and that in reality you are not seeing the top sixteen riders in the world. Whatever the reasons it is failing to ignite the enthusiasm which once surrounded the world championship.