You only have room for so many resource-only cards in your deck, but Digging Deep has tons of combo potential that will spawn entirely new decks built around this effect (shared by White Fox). The number of cards that can discard this from your deck is surprising high, and many are cards you'd be happy to play anyways. A non-exhaustive list includes Weapon X, No Quarter, Global Logistics, Caliban, Piotr's Studio, Repulsor Blast, Aunt May & Uncle Ben, and Cosmo. Of course, it is insane with Domino, and Star-Lord too can place it on top of your deck with his Alter Ego ability. Assuming you also want to play Energy, Genius, Strength, and maybe some Power ofs, I might play a few more resource sinks or card draw to make sure my resources go to use each turn...otherwise you can have some awkward hands. I think we will see some really powerful decks with 3x of this card!
Response: After this card is discarded from the top of your deck, add it to your hand.
You can use Call for Aid and have 0 Avengers Ally in your deck to get all copies of Digging Deep in the deck into your hand at the cost of 1 card + 1 Encounter card. The downside is this immediately triggers a deck reshuffle so all of your Digging Deep will be in the discard pile after the reshuffle and renders future Call for Aid not as useful until another reshuffle. The other downside is you have to play without any Avenger Allies which means missing out on some solid Allies like White Tiger, Kaluu, etc.