MrBitter: Have you played with the deck you posted at all?
Yes! Very, very much!
The card draw is important as a very basic card game mechanic called deck thinning. Jaraxxus is one of your most important win conditions. You absolutely MUST be able to reliable cast him by turn 10, otherwise you're going to have a bad time.
This is why Sense Demons is so invaluable. Also, Voidwalkers are almost never bad. They always serve some great purpose, even if its just buying you one more turn to stick around.
It's also why the card draw from Auctioneers is so important. Most of what you're casting between turn 5 and turn 10 will be removal spells, and if an auctioneer gives you an extra card along with your removal spell, it's creating card advantage for you. You're trading 1 of your cards to eliminate 1 of your opponents cards, and you're also drawing off of your auctioneer. It's 2 for 1 card advantage.
And here's why I think the questing adventurers are important:
They are not your win condition. They CAN snowball and end games. But that's not why they're in the deck. They server multiple purposes:
By virtue of the cards strength, it's almost always going to trade efficiently. IE: You'll never lose it for free. It will always at LEAST trade evenly. (1 for 1)
It FORCES your opponent to react to it. Decks that don't run much removal will have to burn a spell on it. Decks that don't have great creatures to fight with will have to trade with it. It takes away from your opponents ability to deal with your other threats... Namely the Molten Giants.
In other words, if I can force that pesky rogue to burn assassinate on my adventurers, I don't have to worry about it being used on my giants.
Re: Dead cards with high costs -
Don't worry about this. Your summoner spell lets you trade life for card draw. All you have to do is weather storms and survive until late game. Also, because of our magma giants, we don't care about taking damage. We want to hover around 10 HP because it lets us drop 2 giants in 1 turn, and then alexstraza and win in the next. (Unless we're vs. mages)
Additionally, that extra twisting nether is sooo important for those late game situations where the board often spirals out of control in your opponents favor. If you only have a single Twisting Nether, how do you ever justify using it to kill a single dangerous creature?
If you have two, then that's a sacrifice that might make a lot of sense.
Just some more of my feedback on why I use the cards I use. <3