Hmm...today I just found two strange things from my LoT2 run. Firstly, It seems that Rinnosuke's and Komachi's money skill will take effect AFTER the battle. Even if you have equipped the skills, the money shown in the battle result screen stays the same so you have to go check the money after the battle to see the increase.
Secondly, Satori's Spell Recollection skill does not directly increase the spell card cost. Therefore, any increased cost will be ignored as long as you have enough MP to use the spell's base cost.
For instance, Komachi's Narrow Confines' spell costs 6 MP and if you have the skill at Level 1, normally the increased cost will be 6 + (6-1) = 11 MP but the game will still says that it is 6 MP. However, the increased cost will take effect after you use the spell so Satori will lose 11 MP. If Satori has 20 MP then she will now have 9 MP, which would normally make her unable to use Narrow Confines the second time due to increased cost. However, since the game will "drain" extra MP AFTER using the spell, Satori can still cast Narrow Confines, ignoring any extra cost provided that she has enough MP for the original cost. So I guess that's an exploit, yes?