If you have a poor form player, a scout is a gamble but could be overnight boost to the team. Edit- I meant recommended player, scouts are even more costly.

Otherwise, I think the smart choice is green packs training the fast trainers on your main squad. It will improve the squad quality, and you can be smart about how you train their skills. Unless you have all levels of training drills, it also has benefit of increasing your training level, which is like a long term accelerator for team quality and value.