I think it depends on the circuit, I often go to Oulton Park as it's my nearest BSB track and it's often heaving with people there, Cadwell and Brands are really busy as well, also bear in mind not everybody bothers to buy a grandstand ticket and instead prefers to move around the circuit.

As for WSB the crowds are getting worse, putting race one of WSB on the Saturday certainly hasn't helped things either plus a WSB ticket costs more than double what a BSB ticket does and you generally get around ten races on the Sunday at BSB, you're lucky if you get 5 at WSB. Plus WSB on the continent has never been massively popular, even in the Carl Fogarty era the only rounds which were packed were the British rounds and the USA round at Laguna Seca.