Steve,
the attendance stats are not meaningful in themselves (in 1973 the Rome convention was the only one in the country; this year there were several conventions) ... more interesting and suggestive of a remarkable drop in new recruitments is the attendance/baptisms ratio:
in 1973: 3366/57000 (5,90%)
in 2001: 626/80000 (0,78%)
in 2009: 338/70000 (0,48%)
Behemot