At the end of any level, there's a chance of getting an option to remove any card from your deck, at the expense of EXP. Those cards will be permanently removed from your deck for future levels.
I think that discard mechanic would be too complicated. I think it's simpler as is right now: you just use it and spend the charisma. If you don't want it in your deck for good, you need to take the opportunity to remove it using one of the EXP stores at the end of the levels,
Yeah, right now, a discard card option wouldn't provide much value. But, in future updates, I want to add ways to take more value of discarded cards. Right now, there is a card that takes 2 love * the number of cards in your discard pile from any enemy. If you have 5 cards discarded, that's 10 damage for the cost of 2 charisma, which is quite good. You can imagine more cards/clothes like that. Also, new enemy effects that will be more powerful if you have more cards in the discard pile!