I think you asked me about that during September, which at the time I only bought 50 Gems three times for that month and that I was enjoying the game but nothing more. Last month however I got REALLY addicted to SIF because of events, new amazing cards every two weeks, idolising SR cards or above, tackling EX songs, more cards to collect, watching both seasons of the Love Live anime, reading Love Live doujin etc. etc.. Pretty much SIF became an addiction (a good one) and I practically spent significantly a lot of money on it but I feel that every cent going to the game was worth it.
To be honest my luck isn't amazing, but it's good enough that I have 2 URs and a crap load of SRs (the ones idolised are Honoka's, one Hanayo and one Nozomi, all of whom are up there on my favourites). Hell the new SR cards I got took four 10 + 1 draws.