Just need to know if I'm wasting my time here

So I'm a terrible hoarder and I don't even let go of my Idol Cadets. What I'm currently doing is leveling them up along with my few SSRs because I want to know if you get rewarded in any way for reaching a card's max level (I could care less about the IC's affection)

Am I wasting my time and space here? Please say yes so I can fuse these cadets without a single regret.