I think Abomination is fine as it is. 5 
for a 5/5 vanilla creature, not good but not bad either. Abominations were never meant to be played as cards out of mono- decks; they are meant to be created via Mutation, so their stats/cost are fine by me.
Why would someone mono entropy if there are much better mono decks like darkness and fire? And where is the purpose of Abomination in game than? Reason for idea to buff it didn't came from it's "unbalancedness" rather from it being useless. If you read other posts and discussions you will see that nobody disagrees that it "looks" like a good card, but besides looking at it, nobody actually plays it anymore.
Sometimes you create and play with the deck mostly because it is fun rather than because it is powerful. Entropy is fun, no one denies this. If we consider playing only powerful decks, then better upgrade our shards and weapons and every other card we need to farm Gold/Platinum/FalseGods and screw the rest deck/cards. This card is not as bad as many people claim it is, they just have forgotten when they were noobies playing versus PvP1, level 2 AI and level 3 AI. Back then, cards like this were useful, because you hadn't the cash. Some cards are for early gameplay (like dagger) some others for later gameplay (upped shards). Play with Skeletons, Blue Crawlers, Daggers or Abominations for the fun of it in PvP1 or wherever...
By the way, mono-entropy isn't so bad. It makes much easier to play cards like Purple Dragons and Antimmater, it makes unupped Dissipation Shield more durable and you may add a few 
to play Fallen Elves/Druids or whatever. And as I said before, Abominations were meant to be created with Mutation rather than putting them into your deck.
Basicaly you're saying that there's no need for the abomination card itself. You are giving it a Maignant Cell status, since those can be get via aflatoxin, and abominations via mutation. But you can't say "it needs no buff" than, since you're not only nerfing it, but deleteing it.
I also follow the same scheme as you do - upgrading the right shards, and some other good cards, and farming what I can - and that's the point exactly: Rest of the card are useless wheater upgraded or not. Look at Mind flyer - i used unupped version for very long time, and it's almost as good as upgraded. It was one of last cards I upped, it was worth every penny, and I'm using it now. So there are cards that are good even when unnuped, and those that are useless even when upped. We are talking here about general disbalance in game. I can't belive that some people are actually coming up with ideas of buffing darkness (in general) or cards like SoF, while there are like 50 completely unused/useless/underplayed cards. So you're basicaly "going with the flow" no matter where does it go. I belive, and many would agree, that balance is most important factor of the game - after fun-factor ofc. If you have cards that can't even compare to some others cards on "single card basis" you have pure disbalance. Your statement stands in Magic the Gathering terms. Because you NEED 2 different card classes there, desired and undesired cards, cause that "desire" will make you buy more cards. The Elements idea was different, so concept of "useless" cards is kinda pointless here. I'm OK with the fact of different levels of game, and farming. Let say you have some card set as a newbie. And new cards you grind along with rares should make old cards work even better, and not obsolete. SoR did exactly that. It gave new life to pharaons, anubises eternities etc. In MtG terms - you are completely right, but I see this game more like a strategy card game and less like collecting card game.
