Yeah, the strength of the mysteries might not be important at all, depending on where they take the show. Anyway, this series is worth watching for Eru alone, I can't wait for the Eru x Erio crossover fan art.
Eru x Mio and the world will end.
Haven't seen Bungaku Shoujo, but doesn't Hyouka have that whole "classics club" thing going for it?
Based on the series overview, the classics thing will play a role but I think it might just be like those 7 mysteries thing where they run after this stuff but find out they're not really that mysterious after all.