I also like the pre-built decks of SotM and wouldn't want to have to sort through a ton of cards to build my hero every time I want to play a game... but as a personal project I might take a look and see what I can change permanently to add flavor to the alternate characters.
By a twist of fate I have two copies of the game so I can play multiples of the same character in a single game with originals and promos playing side by side (thank you time-travel)... so I'd like to make the different versions a little bit different where it might enhance the theme.
I was going through all the promo cards to see what changes I might make and found that there really aren't that many:
Young Legacy: There's really no need to switch any cards. Her Atomic Glare power really does make it feel like she is the next evolution of Legacy
Rook City Wraith: No need to switch out cards. Her power does really make it feel like she is taking a more active role in investigating her environment.
Redeemer Fanatic: No need to switch out cards. It really is just the same character with a change in world perspective.
Ra: Horus of Two Horizons: No need to switch out cards. Same as above.
Dark Visionary: This one I would like to change one or two cards for this promo to really accentuate the dark side. Maybe change Brain Burn and/or Wrest the Mind so that instead of dealing psychic damage to herself she deals it to another hero... or even to the whole team. I think this would really bring out her dark side. She still fights evil, but she isn't trying as hard to keep her powers in check so as not to hurt her allies.
Team Leader Tachyon: I think I'd get rid of Fleet of Foot (she already has her base power) and maybe instead give her a non-burst card that allows another hero to play a card or something leader-like.
Elemental Absolute Zero: Wouldn't change anything. I think this card kind of gives the feel that AZ finally, after years of fighting and watching his colleagues fall, embraced his destiny to be a hero and learned how to control his suit to deal damage more efficiently. I like it as is and deifnitely changes his game enough.
One-armed Tempest: I don't think I'd change this one either. Other than to get rid of active chain lighting, I am not sure when I'd use that base power either, though. tempest usually has a ton of cards.
Last Stand Wraith: This one is the one I feel really doesn't match her deck anymore. There is an air of desperation to her now... she almost looks like she actually died and came back and is very angry. I just don't see her using a Trust Fund anymore or consulting a Mega Computer, she just seems to want to kick ass... but since I don't really know what her flavor is supposed to be I can't say for sure what changes i would do.
Golem Unity: I like this one, but I have my take on her origin being both the real Unity AND a golem (I posted my thoughts on that elsewhere on the forum) so theonly thing I'd add is the mechanical golem category to her card. The rest of the deck still works fine.
Engine of War Bunker: I think this one works as is too. I kind of like the hulky Fright Train just ignoring the technological complexities of the Bunker modes and just smashing ongoings instead.
The Eternal Haka: No changes. This makes perfect sense thematically too with an old and wise Haka calmly seeking the right tools for the job at hand.
Greatest Legacy: I'd probably just take out Fortitude since it is mentioned that is Finest Legacy's power. I might switch it for something that reduces damage dealt by villain targets (striking fear into the hearts of the enemy). Might modify Superhuman Durability as well. Maybe.
So really there are only 4 that I feel warrant some kind of change... definitely not enough for an expansion.