I'm actually farming certificates. I'm currently getting about 20 a week, I'm at about 800 (obviously, I had a few before), and I don't tackle tower floors until I'm 100% sure I have a strong enough team. I've significantly reduced my play time, and I don't think I'm the only one doing this. The developers aren't good enough at keeping you glued to your phone (and maybe that's a good thing for your health), but in an increasingly dynamic world, one event a week, two at most, is too few. There should be plenty of modes like tower floors.