By stat increasers does that mean Dubloons and Bottled Faeries? + Codestones as you said. I don't think that'd be a bad idea as there's such a small amount of those, and they all clump together, so it wouldn't look very bad in my opinion. And I did notice that some malls actually have their users all stock codestones/dubloons/faeries to get rid of the Training category. I say go for it and increase profits! ;D