This post is full of incorrect information. I would urge new players to disregard it. For one, you don't need to banish any cards that have point value, as points on cards are added up at the end of the game. Don't banish void or enlightened cards from your hand. Don't banish Mystics and Heavy Infantry. They all add points to your score at the end of the game. Secondly, a game of Ascension barely lasts more than 15 turns, not 30 like this post suggests. Remember that you are only going to play 15 hands at the most in most games. The third and most harmful piece of misinformation here is that 75% of the center deck is cards that cost runes. This is simply untrue. It depends on the expansion, but generally about 40% of the deck is monsters. Buying attack is only marginally worse than buying runes, and you absolutely should buy attack if there are a lot of monsters.
I have over 400 wins online, and it is absolutely crucial to know when to buy attack or runes. You will barely ever banish cards from your hand that have point value. Only do it if it is seriously going to clog your hand for multiple turns!
Wow, how mean.
By the way, first of all, I don't really care if I had 2, 3 or 4 Honor Points less in my deck (of course, 5+ HPs are getting a little too many, though), at end of game. I'd rather prefer to avoid useless cards to draw (do you really want to draw a Void Initiate (yes, I'm not linking you cards since you already know them by heart, looking at your online wins you go proud of), a Prodigal, an Arbiter of the Lost and so on, at turn 13-14? I don't really think so) to improve my play turns and buy better cards and defeat stronger Monsters.
I'm not stupid. If I see the Honor Points Pool has ~20% starting value, I stop banishing cards and buy anything with a decent or good Cost-Honor Points value ratio. It would be idiot to banish them at the end of game.
EDIT : I just understood what you meant with "don't banish void or enlightned cards from your hand", and there's a misunderstanding. In my previous post, acquiring was the main verb, while banishing was an adjective. I didn't mean to say "always banish Void and Enlightned cards".
Secondly, the time varies from match to match. If you play a Darkness Unleashed-only game, it surely will last fewer turns, because of the Dark Shards that accelerate game alot. I personally tested it.
It also depends by luck, by the number of players and by the Honor Points Pool you set. I honestly wouldn't be surprised if a match lasted 25+ turns if no banishing cards popped out during it.
Your reference to a maximum of 15 turns is kind of illusorial, unless you're playing with the minimum Honor Points pool setting. I usually run the maximum one. That's why some of my games lasted 25+ turns as well, while many lasted 20-, too. But the average turns duration is 20 to 30.
Thirdly, my percentage was an assumption, but thinking of the expansions all togheter, it gets closer to that percentage, and not to 60%-40%.
And, honestly speaking, I couldn't care less if I didn't defeat a Monster from the Center Row to get a Construct or a Hero. Of course, unless we're talking about Avatar of the Fallen, Samael the Fallen, kythis, Rebel Godling and so on. They surely impact the game a lot. But Monsters like Fettered Soul, Corrosive Widow and so on are just lame to defeat.