Boom // Bust is a card that you don't hear about very often. There was a time when Bloodbraid Elf enabled you to cascade into the two side, but also allowed you just to cast the six side for free. A 3/2 haste with a built-in Armageddon was a cute little gimmick that never really took off. In the wake of the most recent banlist updates, people seem to suddenly be interested in the card again, and it has seen heavy inflation in the past month. Some of this is no doubt due to the fact that Goblin Dark Dwellers lets you cast the six side, again due to access to the two side. Aren't split cards fun!
I've played against Boom // Bust decks a few times recently on MTGO, and the supporting cast of fetchlands, Flagstones of Trokair, Magus of the Tabernacle, and Ghostly Prison seems like it might be real. I don't play decks that are weak to this sort of nonsense, but the efficient mana denial and prison elements actually have the makings of a real deck.
Boom // Bust was a dollar for so long that buying in at $8 feels terrible, but with the Modern PT looming this isn't a bad place to invest. There are very few cards in Planar Chaos that are valuable, though the set is certainly old enough where breakout cards will be difficult to find. If this card sees significant success at PT Oath of the Gatewatch, then expect it to continue to climb in value.
I'm skeptical of Boom // Bust as a buy because the deck looks super gimmicky on its face, but any deck that wants to play it wants to play four copies. If I knew that there were high profile players sleeving up Modern Armageddon then I'd be looking to pick up a few sets.