The Chapada Diamantina national park can be of interest if you live in an horrific megalopolis like Sao Paolo, and need to breath fresh air or just relax without the fear of being mobbed. I suppose a visit would also make sense if you never saw a waterfall, a lagoon, a cave, a river etc. On the other hand, experienced travellers should forget about it and head directly to the Amazon, which is the real deal.