You are completely wrong, I know what I'm talking about. With Cindy, I can practice Tricks for 24 hours and get only ~80k without items equipped and a 70% outfit. Change her to 90% bonus (her max with random fashion items) and that increases to ~90k. Equip 30+30+20% items on top of that, and it increases again ~127k. Equip the 70% outfit plus items, and you only get ~118k. The job only shows ~46k without any bonuses before you start. Everything you do affects the outcome of the training session! How did you not notice this?
In fact, without clothing or items altogether, she gets 48.5k from training, and still the job only shows 46.2k at start, so even that's wrong! There's even some sort of hidden bonus somewhere that isn't showing up.
Anyway, the point is, equipping consumable items WILL give you a training bonus and will not be consumed in the process.
Also, it's beneficial to change the girls' fashion to maximize each stat you are training in AND equip items that compliment the training session. Just don't forget to un-equip the items during a challenge match, because that WILL consume them. After learning about this, it seems items are a lot more valuable than just for consuming during challenge matches.
Sadly, I picked Cindy as my Goto girl, but now it seems she was one of the worst choices, at least for the moment. She only gets more than 70% bonus from fashion in one category, and even then it's only 20% more.
I am almost finished with the charting the stats for each category separately for each girl. Will post results when finished. The info seems useful, so someone who knows how, might want to add the info to the wiki in some form. Of course these number might and probably will change as more fashion items are released.
Cindy's total stamina right now is 615.
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Summary
Training Session - Tricks 24hr: 46.2k (displayed before training session start)
Naked Result: 48.5k
70% Outfit Result: ~80k
90% Random Fashion Result: ~90k
70% Outfit + Items Totaling 80%: ~118k
90% Random Fashion + 80% Items: ~127k