Mana rocks that are now mine, for one turn
We can expect the value of showcase cards to be at least 30% more expensive than the normal version, and thats being conservative
Speaking from the uninformed perspective of someone who's never opened an Unfinity pack, the set looks like it would be fun the first time you tried it, and then never again (outside of an Attraction Commander deck, which admittedly sounds like a laugh)
But the card drawing Fortunes one is clearly the best of the cycle, due to the sheer, raw card advantage that follows
Plus, whenever one or more creature cards hits your graveyard from your library, you get to create a 2/2 Zombie token
As you can see mythics were on track to contribute just under $90 in EV (Estimated Value) to MM15 at launch