I felt like reallocating my powers for Punisher, as I found I was only using a couple of his active skills. So I took my hard-earned splinters that I was saving up for a random character, and bought a Retcon.
Reallocated my skills, then about 20 minutes later got a retcon from a story mission. Whoops!
Yeah, you will probably never need to buy a Retcon with Gs or ES; you can get 1 from each story difficulty on each hero, as regular drops, or as a reward from Fortune Cards.