Mimic Vat is a definite keep
Nasty game winner in the Command Zone
You might not have a spell you can play with all that mana or a way to beat a chump block with your infinitely strong creature
If our opponent cracks a fetch land or shocks themselves, we don't even need the Kor Firewalker, which makes the combo of Boros Reckoner and Volcano Hellion pretty much the same as the recently-banned Splinter Twin combo a turn four, two-card combo
When life totals are redistributed, each player gains or loses the amount of life necessary to equal the other player's life total
In addition to this, a big part of the reason these cards were so popular was because the mana in that Standard format was quite bad, to the extent that you were pretty close to wanting Attune with Aether in your decks even before the energy bonus, but once you have the energy bonus you might as well play Harnessed Lightning, which means you may as well play Rogue Refiner to power up your kill spell, and so on