I agree with WRC that spectators are important (very), but it goes hand in hand with who's competing and with what cars. I think that with more manufacturers, the more interest, as long as the cars are fast and exciting. In the current situation WRC cars are 3s/km slower than last year due to the hard Pirelli tyres and are only apporx 2s/km faster than last years Gp N. S2000 is faster than Gp N, and with a bigger engine (2.5ltr NA) they would be exciting, and without the turbo make fantastic noise verberating through the forests on full song.
There are now more manufactures building S2000 cars than WRC, lots of people still go to see the IRC, so there must be something pulling the crowd.