The only things that make it too powerful
IMO are
1) No other class gets anything like it. If everyone had a "trade resource X to keep a missed encounter power" feat available, it'd be fine.
2) There's no clause in there to prevent temporary hit point abuse. The warlock in the epic game is Star + Fey, but if he were Star + Infernal instead the cost for using the feat would be next to nil a lot of the time, especially for lower level powers like Frigid Darkness and Far Realm Phantasm (steals an action from the enemy and gives a fighter a possible combat Challenge attack, as well as lowering Will defense temporarily).
And yet another word from our sponsors
