Hello.
This might be difficult to change, but I think it's worth to try. :p
Experience system
Every idol gets the level cap. For example, normal idol's cap is 20, silver is 25, golden is 30, and platinum is 35. When the level is up, every attribute of idol will promote automatically. Maybe also gift some points for players to add on freely. To go a step further, we can get points to redeem the trait or cancel the negative trait.
Every idol has a random initial value, and starts with level 1. They get exp from all kinds of activities and level up with enough exp. For now, an idol can only promote their attribute by practicing in the recording studio/dance room. It's inefficiency and making no sense. For example, an idol should get better exp from the concert than the studio. All the activities should offer different exp to the idol. Photoshoot, advertisement, drama, variety show, performance, promotion ect, you know what I mean.
I've played this game over 10 rounds. Everytime I got bored with making lots of money. Yes, I can build my best group with the best idols from the nationwide auditions. Let's say, they are "platinum" idols. Do you get the point? I love my idols from the start. They don't own the great attribute, and most of them are the "normal" idol. For the currently system, it's difficult to promote their attribute to the average value. So usually the ordinary strategy is: pick the normal idols in the beginning, make enouth money, pick the platinum idols. It's like putting the cart before the horse. I think the word "produce" means you train the idols and make them better.
The experience system will make idols better, and make the "old" normal idols more useful.
Thanks for reading.