I made a post a week ago about the problem with the affection system (and some smaller issues).
since then I realized a couple of things I didnt mention in the post - if you finished story and got most of the world girls upgraded and stacked up on affection items simply due to panchinko spamming, it really is no problem to level up affectionlevels of the new girls as you had a good buffer already. the problem really comes when you need to catch up - I didnt finish the story before HH 2.0 was introduced and literally got the three world 7 girls a week after HH 2.0 and since then I try to catch up with the upgrades, especially due to bunny and juliette rank5 being so insanely expensive and unrewarding - I am really close (1.4k affection) away of having all girls at max level, but I also didnt drop any world 8 girls yet
once you upgraded every girl it should not be that much of a fight to upgrade new girls, but to get to that point is such a pain

I would recommand you to read the post I made in regards to money efficency and the bad value of upgrading the effection level of the girls