My first thought would be: Upgrade some heroes to 6-stars.
It's not hard. Just decide in advance what 6-star hero you want, then check to see what 5-star and 4-star heroes you need to build it. Norma is an easy one. To get her to 6-stars, you need 2 x 5-star Normas and 1 5 star Aleria and some other random 5-star chaff. Save the appropriate 3-star heroes to help you build the 4-star heroes. Save them and build the 5-star heroes. Then put them all together to build a 6-star hero.
Sorry if that sounds complex, but it really isn't.