Being at Instant speed means that your open mana need not be wasted at the end of an opponent's turn. Even 1/1 creatures can end up becoming lethal threats if your opponent is finding their threats countered or destroyed. Blue/White Control decks, as well as Jeskai Ascendancy, Jeskai Tokens, and Bant Tokens have use for this card as a supplement to their strategies, as well. Since Secure the Wastes hasn't become yet widely accepted as a staple in any archetype, there's probably room for this instant's value to grow.
Secure the Wastes will survive the spring 2016 rotation, which will take Khans of Tarkir and Fate Reforged from the format, but not Dragons of Tarkir. If you're looking for a card people may still be undervaluing, this could be a good pick. It's probably not going to see any play in Modern, and especially not Legacy or Vintage. It's decent in Commander / EDH token happy decks, but it's not a staple in the format. Still, I like this as a decent value rare all the way until it rotates from Standard in late 2016. It should find plenty more homes before then.