You know as you said in your above post, it's pretty useless for me now because I leveled up the Offspring Fling! Badge, so I think that this is the safest way to sell it! And you are not dumb, you just were curious!
I figured I'd open it as boosters can cough up a foil, but the moment after I clicked the unpack button I remembered that Psychonauts cards are next to worthless and I likely would have made (a little) more money selling the pack itself instead of the individual cards.