1. Instead of Monday, farm them on events. There are monthly events to do 60 plot/elite missions a day and weekly events like current Time Limited Shop one which give bonus stuff for doing plot/elite missions.
2. Always save summon/seal scrolls to use during rebate, the more patient you are the more you get back for free, if you use 50 scrolls during rebate you get like 4 scrolls for free, but if you do 300 rebate you get 50+ back. Also in general each new treasure is stronger then last, so unless you want specific ninja it's best to pull in one of the later ones.