With Standard rotation going back to a two-year cycle, a ton of Azorius Midrange in the Top 8 of GP Kuala Lumpur, and Bant Spirits winning the Milwaukee Open, it was a great weekend for Selfless Spirit.
Eldritch Moon cards are definitely good targets right now, though I think that at $12 I'm more interested in selling Spirits than buying. The card is great, though the power of the Azorius decks seems overstated to me, and though the deck will continue to perform on some level I can't imagine Selfless Spirit being able to gain more than 50% more value, and I think I'm being generous there. This weekend was something of a perfect storm for short-term inflation.
Kuala Lumpur was barely over 700 players, Bant Spirits isn't about to take over Modern, and there are plenty of Selfless Spirits out there. I don't expect it to be longer before the price starts to drops.