700 gold is almost 2 weeks worth of quests though. 40gold + 10gold for 3 wins a day leads to 50 gold a day. Sometimes, you get 60 gold quests, but it's still not a very fast rate to earn 2800 gold for 4 wings.
It depends on if you bank your quests or take them right away. Ideally, you take the 60s right away, reject the 40s, and avoid completing them until you get another 60 and can use that day's reject on an old 40. I feel like this way, I get almost as many 60s as 40s. Basically you get to complete 7 out of 14 offered quests, and ~3 of those should be for 60 gold.
It's also possible that by doing the wings you complete some Naxx-specific quests (like the initial ones when you started playing the game), which gives more gold. I think if you play a lot (like you're able to complete all your quests), it shouldn't take more than 2-3 extra weeks of saving to play Naxx on game gold.