Best of all, since there’s a lot of Scry in the deck, between the Temple scry-lands and Serum Visions, oftentimes you’ll know what the top card of your deck is. Ad Nauseum allows you to add cards to your hand as many times as you like, as long you can afford to pay the life cost. Lands have a converted mana cost of 0 so those cost you nothing.
Being a tutor of sorts, it’s not surprising to see this card jump from a $2 rare to over $5. Foils are growing quickly, too, but copies can still be had for $4-5, as of July 22, 2015. This would obviously make foils a better buy right now. Being a card that sees Modern play in this deck, and some occasional play in legacy, Spoils of the Vault is a strong foil pickup. The only possible drawback is that part of the Ad Nauseum combo gets banned in Modern - which is something that has been discussed in the community, but it hasn’t been yet, so it’s doubtful.