Maybe calling the mechanic something like "Alchemy", but the idea is to transmute acquired buff cards into other buff cards of the same rank. For example, I never use the "Splash" cards. Literally never because I have Merci's "Deflect Evil" so well-buffed. For me, specifically, they are by far the most useless. However, I do like stocking up on warps to stock up on event currency. I will literally never have a use for Splash cards, but more warps are always welcomed.

That said, part of the game is the random element of not knowing what cards you'll get from chests. Being able to freely transmute would negate the random chance of chest drops. To keep it from being entirely imbalanced, there should be some kind of cost to transmute items. For example, the transmuting process would not be 1-for-1. Rather, there would be set amounts to transmute at once (10, 20, 50, 100, etc at once) but the player would receive 50-70% of the amount they transmuted. So transmuting 100 "Blaze" cards into warps would result in 70 "Delorean"s. Since warps do not have common-tier, other common-tier buffs would not be able to transmute into warps.

I'm pretty sure warps drop from normal chests. Uncommons and rares. The epic "Quantum Leap"s only drop from jeweled chests.

Just a very random idea, inspired by your main post:

What if we could dissolve any buff card into small amount of crafting materials (rarity of buff card = rarity of materials, similar to duplicate gear)?
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What if we could create any buff card (except maybe warp cards, as Teschio pointed out) from crafting materials?

To be able to convert excess buff cards into something more useful sounds heavenly. In almost two years of play I have only seriously used my buffs twice. Once was just because I wanted to see what would happen and the other was pushing for the area 1k achievement.

Even if we could just do a trade up and trade down the same buff type. The idea of converting all the saws, eyeballs, and swords into boots sounds better though.