Engineered Explosives has been a great sideboard option in Modern for a very long time, though it has never been terribly expensive. When the card was reprinted in Modern Masters it felt like the card would never be worth more than $20. Recently, EE has eclipsed that price.
With Elves winning the Somerset Invitational and Death's Shadow Zoo becoming increasingly popular, EE is looking great as a sideboard option, though this price movement is likely more based around the card being difficult to reprint. Sunburst isn't coming back anytime soon, especially with converge being used so recently, which means that EE won't be getting reprinted in a Standard legal set for at least the foreseeable future. Conspiracy was the set where the reprints apparently got dumped, and as such the card will not be showing up until at least the next Modern Masters set. Theoretically it could show up in a Commander product, though given the way that the card lines up with that format this would amaze me.
Buylist prices have not grown to match the spike, and while copies of EE are on TCGPlayer for $35+ in both versions, buylist prices are less than half of that. Seeing as EE is a sideboard card and that it's unclear where buylists will settle, I would be apprehensive about acquiring even the "cheaper" copies on the market, and wouldn't be terribly excited about trading into these either. The demand on this card isn't substantial enough to justify such a high price tag, and an eventual reprint would shred that price. I am much more interested in trying to sell off the copies that I already own.