AMR/AML -what special ability shall I train for them

[Toxcatl]

If you farm rests every day and do the training methodically, then I'd say you need SA for your long-term players.

Quality is a real b17ch in this game. You can have 100% team or 120% team, or even 140% team, but there will be no real difference. The gameplay will be the same. The game is slightly smarter than simple "get more quality", because on the next level you will have matching opponents regardless of your team's quality. 115-140% team is enough for almost everything, including playing in Platinum division, and we can afford having SA with this quality.

SA is a way to make your team stronger without gaining actual quality, that's why it's valuable. It is the same thing as mutantism: squeezing every drop from the current team quality. Getting SA when the player has low quality is very easy, so on the high-quality level (120%+) SA will mean just a few missing percents, not a full star. SA worth it, as would anything else that provides any bonus without gaining the actual quality.

In other words, it is better to have 110-130% team with SAs than 120-140% without SA (I bet the difference is significantly smaller), because on the long run your average opponent will match your quality anyway. And it is better to have a small bonus than don't.