Please stop hoarding them as though every account only gets 9 and no more. The threads today saying "nobody would ever use an elder kai on (extremely overpowered top tier support for their main team) instead of using it on (top tier damagers for team they never use)" is crazy to me.

You will always have more. If you're choosing between raising the SA of a card on your main team or a card on a team you never use, the main team cards win always no matter how good the random card in your box is.

If you play super STR, and you have the ideal STR team and run it in everything, why would you raise Super 17s SA first? Your INT Kid Buu you're gonna use three times ever doesn't need to be SA10 before your STR subs that you use multiple times every single day.

If you want to talk about "efficiency" the efficient thing to do is raise the most used cards. Either way, Kai's are forever.