Two Rakdos legends, Alesha, Who Laughs at FateAlesha, Who Laughs at Fate and Chainer, Nightmare AdeptChainer, Nightmare Adept (22,597 and 62,178 decks, respectively), can recur something if it's big enough, and by discarding a card and paying other costs, respectively
Red Mage's Rapier Rarity: Common TYPE: Artifact SUBTYPE: Equipment CMC: 2 Mana cost: USD: $0.14 EUR: 0.08 TIX: 0.03 EDHREC RANK: 8824 Job select (When this Equipment enters, create a 1/1 colorless Hero creature token, then attach this to it.) Equipped creature has "Whenever you cast a noncreature spell, this creature gets +2/+0 until end of turn" and is a Wizard in addition to its other types
As such, experimental data indicates that the experimental probability of opening an Enchanted card is likely around 1%
Thats not to say that you wont find powerful cards in a Set Booster indeed, each pack of 12 cards (plus two bonus, non-game cards such as art cards) contains 1-5 cards at the Rare or higher rarity level, making them a more appealing product in some ways than, say, Draft Boosters
