I've read an article about arena and I do agree with one point they made in the article is that now is a pretty bad time to do arenas. A lot of people are saving up gold for Naxx, including a lot of more casual players, and the pool of players currently in arena is some people who don't know about Naxx at all or plan on buying it with money and a lot of people who have more gold than they need, which for the most part are arena players with high win rates. Which means currently arena is a lot harder than it was a few months ago(especially during iPad release), because there's not as many bad arena players.
Now obviously this is purely conjecture but I've done 2 arena runs myself the other day and I might have been unlucky but I didn't see anyone playing really shit cards and stuff. The guy making the point had a 70+% winrate before but for the 12runs he did recently he was quite a lot lower, with an average of 5wins only.
Arenas also require a certain amount of base knowledge of value of the cards and strategies as well as more than one class, so depending on the effort you want to put in, it might be better to just spend your gold on packs right away.