Quest potions are definitely worthwhile, from everything that I've seen. Just wait until one of those pulls is a gold or a legendary, and that math looks way different.

The higher in brackets you go, the more rewards chests from each daily, so the potions add a lower % of increased chests, BUT your chests also offer better rewards the higher in the brackets you are...

From my own play, and chatting/observing a few other people, the Quest Potions seem to be one of the best investments in the game right now.

Just be sure to use credits, not DEC, until the price goes back to $0.001