You make a good point about the achievements. Knowing about them would not only allow players to plan ahead, it would also incentivise them to get familiar with cards and game mechanics before jumping into either arena or ranked play. An achievement tab should do the trick.
I don't mean to step on your toes, Clarste, but I take issue with your numbers. First of all, two arena runs yield at the very, very least 200g in packs. It's actually highly unlikely not to get more, but let's work with this bleak scenario. You now have 2 packs and the information that you're not all that good at drafting. Now, assuming you persist and want to play another arena, you need 150g.
You'll get that considerably faster than the 10g per hour you put forward, because you neglected to take quests into account. 40g every day is not to be sneezed at, especially when you can do it while playing the deck you wanted to try anyway. Again, we're being modest here - there are quests with 60g rewards and one that yields a whopping 100g. I think fitting only six matches in an hour is a little on the low side as well, but I haven't timed my matches. My gut says that number ought to be higher, but that's neither here nor there. You could of course always play fast decks in constructed, which would allow you to finish more games. In fact, most gold grinding guides recommend precisely that.
I'm not going to argue how many cards out of a pack are worthless, because that's largely a matter of opinion. If you're trying to build one specific deck, you need to get lucky. If you're just trying to collect, every card is fair game. And if you have multiple decks in the works, which is likely considering the number of heroes, most cards will be useful in some fashion. I like that even a completely dead card is still worth dust.
I'm a little surprised that you mentioned Ysera and Mekkatorque, honestly. While Ysera is certainly powerful, a considerable number of matches is already decided before she comes into play. She might be one of the best legendaries around, but I can't remember that I actually thought "I would've won if it weren't for that dragon". Mekkatorque, on the other hand, is not exactly a great card. You're more likely to lose to one of the 6 mana charge or taunt minions, half of which are basic.
Mind you, I wouldn't complain if rewards were larger. But I can't help feeling that a lot of players severely misjudge the value of big, shiny, rare cards. As a matter of fact, you don't need to spend anything. Hearthstone offers you a lot of freebies just for playing the game. If you manage those resources smartly, you'll reliably earn more gold and more packs, which, again, you don't desperately need since most successful decks only splash non-basics.