You could switch some (%) rewards value from quests and give it as a bonus for consecutive daily logins. Probably with few milestones, that would give slightly better rewards but reset at the end of the month - to build up a better motivation.
These thing wouldn't hurt economy, if you do a calculation and deduct average daily-reward-by-time amount from average daily-login-by-time. But they motivate people to come to the game and at least read a news or play a match when they otherwise wouldn't.
It just came to my mind when I literally accidently read about new season and new card system and got hyped about it.

If there were daily login rewards I wouldn't miss such big news for sure!