Baseball attendance is down 2.9 percent, but the Miami Marlins alone account for 40 percent of the decline in tickets sold, and the weather in many places has been brutal. Much has been made about low attendance at interleague games this week, with the Mets and Yankees, for instance, failing to attract their usual sellouts.
People use those crowds as a proxy for baseball's popularity, but you have to understand there is a story behind those interleague numbers. Now that MLB has moved to two 15-team leagues, the little accounting trick baseball used to sell the popularity of interleague play no longer applies. In past years baseball would make sure to schedule as many interleague series as possible on weekends, when school was out (especially the "natural rival" series.) MLB then could point to the "increased attendance" of interleague games as the fans' way of voting their approval of interleague play.
But those games drew well in great part because of when they were played. The toughest tickets to sell are weeknight games while school is in session -- thus the empty seats this week in New York. So don't be so quick to think attendance at interleague games is a problem or the "novelty" of it has worn off. With interleague games all year, MLB no longer can gerrymander the interleague schedule the way it did before.